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21fe9edd96652b00861b454524f047fb967a05d98600491f1e3f7859631eb891
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2026-01-21T00:00:00-05:00
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Information transport and transport-induced entanglement in open fermion chains
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arXiv:2601.14153v1 Announce Type: new Abstract: Understanding the entanglement dynamics in quantum many-body systems under steady-state transport conditions is an actively pursued challenging topic. Hydrodynamic equations, akin to transport equations for charge or heat, would be of great interest but face severe challenges because of the inherent nonlocality of entanglement and the difficulty of identifying conservation laws. We show that progress is facilitated by using information as key quantity related to - but distinct from - entanglement. Employing the recently developed "information lattice" framework, we characterize spatially and scale-resolved information currents in nonequilibrium open quantum systems. Specifically, using Lindblad master equations, we consider noninteracting fermion chains coupled to dissipative reservoirs. By relating the information lattice to a noise lattice constructed from particle-number fluctuations, we show that information is experimentally accessible via noise easurements. Similarly, local information currents can be obtained by measuring particle currents, onsite occupations, and covariances of particle numbers and/or particle currents. Using the fermionic negativity to quantify bipartite entanglement, we also study transport-induced entanglement and its relation to information currents. For a clean particle-hole symmetric chain, we find that information currents are shielded from entering the information lattice. Impurities or particle-hole asymmetry break this effect, causing information current flow and entanglement between end segments of the chain. Our work opens the door to systematic investigations of information transport and entanglement generation in driven open quantum systems far from equilibrium.
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https://arxiv.org/abs/2601.14153
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Academic Papers
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b6cf979e7c6e434880bebd79454885194b1e64bd66cedd61f6bb695a9093935f
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2026-01-21T00:00:00-05:00
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Localizable Entanglement as an Order Parameter for Measurement-Induced Phase Transitions
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arXiv:2601.14185v1 Announce Type: new Abstract: We identify localizable entanglement (LE) as an order parameter for measurement-induced phase transitions (MIPT). LE exhibits universal finite-size scaling with critical exponents that match previous MIPT results and gives a nice operational interpretation connecting MIPTs to classical percolation. Remarkably, we find that LE decays exponentially with distance in the area-law phase as opposed to being essentially constant for the volume-law phase thereby, discover an intrinsic length scale $\xi_E$ that diverges at the critical measurement probability $p_c$. While classical percolation transition captures successful transport across a network, MIPT as characterized by LE can be interpreted as quantifying the amount of quantum teleportation between two given nodes in a quantum circuit. Building on this insight, we propose a two-ancilla protocol that provides an experimentally accessible readout of entanglement redistribution across the transition.
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https://arxiv.org/abs/2601.14185
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Academic Papers
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b0c3bf9b7ae53c03bb2370c79751ec92235dd58806dde56b5f539434460c3e4f
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2026-01-21T00:00:00-05:00
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Device-independent quantum memory certification in two-point measurement experiments
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arXiv:2601.14191v1 Announce Type: new Abstract: Quantum memories are key components of emerging quantum technologies. They are designed to store quantum states and retrieve them on demand without losing features such as superposition and entanglement. Verifying that a memory preserves these features is indispensable for applications such as quantum computation, cryptography and networks, yet no general and assumption-free method has been available. Here, we present a device-independent approach for certifying black-box quantum memories, requiring no trust in any part of the experimental setup. We do so by probing quantum systems at two points in time and then confronting the observed temporal correlations against classical causal models through violations of causal inequalities. We perform a proof-of-principle experiment in a trapped-ion quantum processor, where we certify 35 ms of a qubit memory. Our method establishes temporal correlations and causal modelling as practical and powerful tool for benchmarking key ingredients of quantum technologies, such as quantum gates or implementations of algorithms.
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https://arxiv.org/abs/2601.14191
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Academic Papers
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3a8debfd654b45a4704afcbf870d44b82db661670ebd316e9ab76472c6253f3b
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2026-01-21T00:00:00-05:00
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Native linear-optical protocol for efficient multivariate trace estimation
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arXiv:2601.14204v1 Announce Type: new Abstract: The Hong-Ou-Mandel test estimates the overlap between spectral functions characterizing the internal degrees of freedom of two single photons. It can be viewed as a photon-native protocol that implements the well-known quantum SWAP test. Here, we propose a native linear-optical protocol that efficiently estimates multivariate traces of quantum states called Bargmann invariants, which are ubiquitous in quantum mechanics. Our protocol may be understood as a photon-native version of the cycle test in the circuit model, which encompasses many-photon multimode quantum states. We show the protocol is sample-efficient and discuss applications, such as generalized suppression laws, efficient quantum kernel estimation for quantum machine learning, eigenspectrum estimation, and the characterization of multiphoton indistinguishability.
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https://arxiv.org/abs/2601.14204
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Academic Papers
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50870d550f29d7049066347c6c9b1c686fe81be13cc50f9f2e9e559bde4a7f14
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2026-01-21T00:00:00-05:00
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Locality forces equal energy spacing of quantum many-body scar towers
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arXiv:2601.14206v1 Announce Type: new Abstract: Quantum many-body scars are non-thermal eigenstates embedded in the spectra of otherwise non-integrable Hamiltonians. Paradigmatic examples often appear as quasiparticle towers of states, such as the maximally ferromagnetic spin-1/2 states, also known as Dicke states. A distinguishing feature of quantum many-body scars is that they admit multiple local "parent" Hamiltonians for which they are exact eigenstates. In this work, we show that the locality of such parent Hamiltonians strongly constrains the relative placement of these states within the energy spectrum. In particular, we prove that if the full set of Dicke states are exact eigenstates of an extensive local Hamiltonian, then their energies must necessarily be equally spaced. Our proof builds on recent results concerning parent Hamiltonians of the $W$ state, together with general algebraic structures underlying such quasiparticle towers. We further demonstrate that this equal spacing property extends to local Hamiltonians defined on arbitrary bounded-degree graphs, including regular lattices in any spatial dimension and expander graphs. Hamiltonians with $k$-local interactions and a bounded number of interaction terms per site are also encompassed by our proof. On the same classes of graphs, we additionally establish equal spacing for towers constructed from multi-site quasiparticles on top of product states. For the towers considered here, an immediate corollary of the equal spacing property is that any state initialized entirely within the quantum many-body scar manifold exhibits completely frozen entanglement dynamics under any local Hamiltonian for which those scars are exact eigenstates. Overall, our results reveal a stringent interplay between locality and the structure of quantum many-body scars.
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https://arxiv.org/abs/2601.14206
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9d3b32c30deedd7c968fbd17b0749a08510e9a40f27d1060c040fd0e0bd02b58
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2026-01-21T00:00:00-05:00
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Group Fourier filtering of quantum resources in quantum phase space
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arXiv:2601.14225v1 Announce Type: new Abstract: Recently, it has been shown that group Fourier analysis of quantum states, i.e., decomposing them into the irreducible representations (irreps) of a symmetry group, enables new ways to characterize their resourcefulness. Given that quantum phase spaces (QPSs) provide an alternative description of quantum systems, and thus of the group's representation, one may wonder how such harmonic analysis changes. In this work we show that for general compact Lie-group quantum resource theories (QRTs), the entire family of Stratonovich-Weyl quantum phase space representations-characterized by the Cahill-Glauber parameter $s$-has a clear resource-theoretic and signal-processing meaning. Specifically, changing $s$ implements a group Fourier filter that can be continuously tuned to favor low-dimensional irreps where free states have most of their support ($s=-1$), leave the spectrum unchanged ($s=0$), or highlight resourceful, high-dimensional irreps ($s=1$). As such, distinct QPSs constitute veritable group Fourier filters for resources. Moreover, we show that the norms of the QRT's free state Fourier components completely characterize all QPSs. Finally, we uncover an $s$-duality relating the phase space spectra of free states and typical (Haar-random) highly resourceful states through a shift in $s$. Overall, our results provide a new interpretation of QPSs and promote them to a signal-processing framework for diagnosing, filtering, and visualizing quantum resources.
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https://arxiv.org/abs/2601.14225
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Academic Papers
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93d0b3e4fea1527d6d504bd0533ba892f0292bd4b476b7c816ed9dbe00c5b814
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2026-01-21T00:00:00-05:00
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Deep Learning Approaches to Quantum Error Mitigation
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arXiv:2601.14226v1 Announce Type: new Abstract: We present a systematic investigation of deep learning methods applied to quantum error mitigation of noisy output probability distributions from measured quantum circuits. We compare different architectures, from fully connected neural networks to transformers, and we test different design/training modalities, identifying sequence-to-sequence, attention-based models as the most effective on our datasets. These models consistently produce mitigated distributions that are closer to the ideal outputs when tested on both simulated and real device data obtained from IBM superconducting quantum processing units (QPU) up to five qubits. Across several different circuit depths, our approach outperforms other baseline error mitigation techniques. We perform a series of ablation studies to examine: how different input features (circuit, device properties, noisy output statistics) affect performance; cross-dataset generalization across circuit families; and transfer learning to a different IBM QPU. We observe that generalization performance across similar devices with the same architecture works effectively, without needing to fully retrain models.
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https://arxiv.org/abs/2601.14226
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Academic Papers
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9161602c9ad9a16699a57a7b08ce1454bfd4c3273970257c87823eee37b0c4c3
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2026-01-21T00:00:00-05:00
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Homogeneous Microwave Delivery for Quantum Sensing with Nitrogen-Vacancy Centers at High Pressures
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arXiv:2601.11725v1 Announce Type: cross Abstract: Nitrogen vacancy (NV) centers have been demonstrated as a useful tool in high pressure environments. However, the geometry and small working area of the diamond anvil cells (DACs) used to apply pressure present a challenge to effective delivery of microwave (mw) fields. We designed and characterized a novel slotted design for mw transmission to nitrogen-vacancy centers (NVs) in a diamond anvil cell via zero-field and in-field optically detected magnetic resonance (ODMR) measurements across pressures between 1 and 48 GPa. The mw fields experienced by NVs across the diamond culet was calculated from Rabi frequency and found to be higher and more uniform than those generated by an equivalent simple mw line, which will improve performance for wide-field, high-pressure measurements to probe spatial variations across samples under pressure.
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https://arxiv.org/abs/2601.11725
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8449c00ecaa93419e030f91605a8d1cdfc768e6c624e36f01fb15b16cdc80404
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2026-01-21T00:00:00-05:00
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Quantum Kernel Machine Learning for Autonomous Materials Science
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arXiv:2601.11775v1 Announce Type: cross Abstract: Autonomous materials science, where active learning is used to navigate large compositional phase space, has emerged as a powerful vehicle to rapidly explore new materials. A crucial aspect of autonomous materials science is exploring new materials using as little data as possible. Gaussian process-based active learning allows effective charting of multi-dimensional parameter space with a limited number of training data, and thus is a common algorithmic choice for autonomous materials science. An integral part of the autonomous workflow is the application of kernel functions for quantifying similarities among measured data points. A recent theoretical breakthrough has shown that quantum kernel models can achieve similar performance with less training data than classical models. This signals the possible advantage of applying quantum kernel machine learning to autonomous materials discovery. In this work, we compare quantum and classical kernels for their utility in sequential phase space navigation for autonomous materials science. Specifically, we compute a quantum kernel and several classical kernels for x-ray diffraction patterns taken from an Fe-Ga-Pd ternary composition spread library. We conduct our study on both IonQ's Aria trapped ion quantum computer hardware and the corresponding classical noisy simulator. We experimentally verify that a quantum kernel model can outperform some classical kernel models. The results highlight the potential of quantum kernel machine learning methods for accelerating materials discovery and suggest complex x-ray diffraction data is a candidate for robust quantum kernel model advantage.
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https://arxiv.org/abs/2601.11775
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Academic Papers
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ca1a5ee24c1e0114a679030c7001bd982fffdfc3417df8408b26e285cb5f06c8
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2026-01-21T00:00:00-05:00
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Trainability-Oriented Hybrid Quantum Regression via Geometric Preconditioning and Curriculum Optimization
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arXiv:2601.11942v1 Announce Type: cross Abstract: Quantum neural networks (QNNs) have attracted growing interest for scientific machine learning, yet in regression settings they often suffer from limited trainability under noisy gradients and ill-conditioned optimization. We propose a hybrid quantum-classical regression framework designed to mitigate these bottlenecks. Our model prepends a lightweight classical embedding that acts as a learnable geometric preconditioner, reshaping the input representation to better condition a downstream variational quantum circuit. Building on this architecture, we introduce a curriculum optimization protocol that progressively increases circuit depth and transitions from SPSA-based stochastic exploration to Adam-based gradient fine-tuning. We evaluate the approach on PDE-informed regression benchmarks and standard regression datasets under a fixed training budget in a simulator setting. Empirically, the proposed framework consistently improves over pure QNN baselines and yields more stable convergence in data-limited regimes. We further observe reduced structured errors that are visually correlated with oscillatory components on several scientific benchmarks, suggesting that geometric preconditioning combined with curriculum training is a practical approach for stabilizing quantum regression.
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https://arxiv.org/abs/2601.11942
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2f0888560a91e4ec537da94cf97ac016f1baad8ce234db0b8c51b1b29f7802d5
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2026-01-21T00:00:00-05:00
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Measurement-induced crossover in quantum first-detection times
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arXiv:2601.12102v1 Announce Type: cross Abstract: The quantum first-detection problem concerns the statistics of the time at which a system, subject to repeated measurements, is observed in a prescribed target state for the first time. Unlike its classical counterpart, the measurement back action intrinsic to quantum mechanics may profoundly alter the system dynamics. Here we show that it induces a distinct change in the statistics of the first-detection time. For a quantum particle in one spatial dimension subject to stroboscopic measurements, we observe an algebraic decay of the probability of the first-detection time if the particle is free, an exponential decay in the presence of a confining potential, and a time-dependent crossover between these behaviors if the particle is partially confined. This crossover reflects the purely quantum nature of the detection process, which fundamentally distinguishes it from the first-passage problem in classical systems.
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https://arxiv.org/abs/2601.12102
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61efd2501516d6d0ef015b68d4ca782f7ab4d0d13b3d6224c281fdae36b12e7f
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2026-01-21T00:00:00-05:00
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Quantum State Preparation of Ferromagnetic Magnons by Parametric Driving
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arXiv:2601.12833v1 Announce Type: cross Abstract: We propose a method to prepare and certify Gaussian quantum states of the ferromagnetic resonance spin-wave modes in ferromagnets using a longitudinal drive. Contrary to quantum optics-based strategies, our approach harnesses a purely magnonic feature - the spin-wave nonlinearity - to generate magnon squeezing. This resource is used to prepare vacuum-squeezed states, as well as entangled states between modes of different magnets coupled via a microwave cavity. We propose methods to detect such states with classical methods, such as ferromagnetic resonance or local pickup coils, and quantify the required detection efficiency. We analytically solve the case of ellipsoidal yttrium iron garnet ferrimagnets, but our method applies to a vast range of shapes and sizes. Our work enables quantum magnonics experiments without single-magnon sources or detectors (qubits), thus bringing the quantum regime within reach of the wider magnonics community.
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https://arxiv.org/abs/2601.12833
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a30fdb7ea9872d8ff4f60a0ea901aabbca2edb5acd6845d708da5b36e897206b
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2026-01-21T00:00:00-05:00
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The Anderson impurity model from a Krylov perspective: Lanczos coefficients in a quadratic model
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arXiv:2601.13255v1 Announce Type: cross Abstract: We study the Lanczos coefficients in a quadratic model given by an impurity interacting with a multi-mode field of fermions, also known as single impurity Anderson model. We analytically derive closed expressions for the Lanczos coefficients of Majorana fermion operators of the impurity for different structures of the coupling to the hybridisation band at zero temperature. While the model remains quadratic, we find that the growth of the Lanczos coefficients structurally depends strongly on the chosen coupling. Concretely, we find $(i)$ approximately constant, $(ii)$ exactly constant, $(iii)$ square root-like as well $(iv)$ linear growth in the same model. We further argue that in fact through suitably chosen couplings, essentially arbitrary Lanczos coefficients can be obtained in this model. These altogether evince the inadequacy of the Lanczos coefficients as a reliable criterion for classifying the integrability or chaoticity of the systems. Eventually, in the wide-band limit, we find exponential decay of autocorrelation functions in all the settings $(i)-(iv)$, which demonstrates the different structures of the Lanczos coefficients not being indicative of different physical behavior.
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https://arxiv.org/abs/2601.13255
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Academic Papers
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b43170006d76362f1d3c6c5ebe0e7a45bafd3637f83540ac5bfc8c6486fd2aa7
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2026-01-21T00:00:00-05:00
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Two-Point Stabilizer R\'enyi Entropy: a Computable Magic Proxy of Interacting Fermions
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arXiv:2601.13314v1 Announce Type: cross Abstract: Quantifying non-stabilizerness (``magic'') in interacting fermionic systems remains a formidable challenge, particularly for extracting high order correlations from quantum Monte Carlo simulations. In this Letter, we establish the two-point stabilizer R\'enyi entropy (SRE) and its mutual counterpart as robust, computationally accessible probes for detecting magic in diverse fermionic phases. By deriving local estimators suitable for advanced numerical methods, we demonstrate that these metrics effectively characterize quantum phase transitions: in the one-dimensional spinless $t$-$V$ model, they sharply identify the Luttinger liquid to charge density wave transition, while in the two-dimensional honeycomb lattice via determinant quantum Monte Carlo, they faithfully capture the critical exponents of the Gross-Neveu-Ising universality class. Furthermore, extending our analysis to the fractional quantum Hall regime, we unveil a non-trivial spatial texture of magic in the Laughlin state, revealing signatures of short-range exclusion correlations. Our results validate the two-point SRE as a versatile and sensitive diagnostic, forging a novel link between quantum resource theory, critical phenomena, and topological order in strongly correlated matter.
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https://arxiv.org/abs/2601.13314
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dd116a16f979e204dac69eeaf60677714eedd836cb119ded42a0c23dd45e4786
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2026-01-21T00:00:00-05:00
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Inferring rotations using a bosonic Josephson junction
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arXiv:2601.13344v1 Announce Type: cross Abstract: Rotation and quantum tunneling are fundamental concepts in physics, and their interplay in the ultracold atomic systems is of particular interest. In this theoretical work, we explore how tunneling dynamics in a bosonic Josephson junction are modified when the system is placed in a rotating, non-inertial frame. We show that the tunneling dynamics of ultracold bosons in a two-dimensional double-well potential offer an alternative pathway for inferring the rotation frequency. Using the mean-field and many-body analyses, we demonstrate that rotation strongly modifies the tunneling time period as well as the momentum and angular momentum dynamics. When the rotation axis passes through the center of the double well, the observables show distinct dynamical responses with increasing rotation frequency, enabling the rotation frequency to be assessed from changes in the tunneling dynamics. When the potential is displaced from the rotation axis, the rotation induces asymmetric tunneling and partial self-trapping, allowing both the rotation frequency and the displacement to be inferred. We further show that for an off-centered double well, the tunneling dynamics exhibit a pronounced orientation dependence, enabling the orientation of the double well to be inferred from the observed dynamics. The many-body analysis further shows that the depletion dynamics are strongly influenced by rotation, providing an additional tool for assessing the rotation frequency. Finally, we study the effect of time-dependent rotation in which the double well is gradually set into motion in the laboratory frame and identify distinct dynamical signatures that depend sensitively on the switching time. Together, these results establish a comprehensive framework for inferring the rotation frequency, radial displacement, and orientation directly from the tunneling dynamics.
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https://arxiv.org/abs/2601.13344
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e917fa19699f54857c54738e0bf4c851a27791b060f191a6c4a1b2d67bdaaec6
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2026-01-21T00:00:00-05:00
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Loopless multiterminal quantum circuits at odd parity
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arXiv:2601.13369v1 Announce Type: cross Abstract: We theoretically investigate loopless multiterminal hybrid superconducting devices at odd fermion parity with time-reversal symmetry. We find that the energy-phase relationship has a double minimum corresponding to opposite windings of the superconducting phases. Spin-orbit coupling adds multi-axial spin splittings, which contrasts with two-terminal devices where spin dependence is uniaxial. Capacitive shunting localizes quantum circuit states in the wells and exponentially suppresses their splitting. For weak spin-orbit strength, the system has a four-dimensional spin-chirality low-energy subspace which can be universally controlled with electric fields only.
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https://arxiv.org/abs/2601.13369
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Academic Papers
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f4ef5d4b679dee60bb909a4ef88d752c5139ecc105b4c9a258a31fcd9c178e37
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2026-01-21T00:00:00-05:00
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Onset of thermalization of q-deformed SU(2) Yang-Mills theory on a trapped-ion quantum computer
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arXiv:2601.13530v1 Announce Type: cross Abstract: Nonequilibrium dynamics of quantum many-body systems is one of the main targets of quantum simulations. This focus - together with rapid advances in quantum-computing hardware - has driven increasing applications in high-energy physics, particularly in lattice gauge theories. However, most existing experimental demonstrations remain restricted to (1+1)-dimensional and/or abelian gauge theories, such as the Schwinger model and the toric code. It is essential to develop quantum simulations of nonabelian gauge theories in higher dimensions, addressing realistic problems in high-energy physics. To fill the gap, we demonstrate a quantum simulation of thermalization dynamics in a (2+1)-dimensional $q$-deformed $\mathrm{SU}(2)_3$ Yang-Mills theory using a trapped-ion quantum computer. By restricting the irreducible representations of the gauge fields to the integer-spin sector of $\mathrm{SU}(2)_3$, we obtain a simplified yet nontrivial model described by Fibonacci anyons, which preserves the essential nonabelian fusion structure of the gauge fields. We successfully simulate the real-time dynamics of this model using quantum circuits that explicitly implement $F$-moves. In our demonstrations, the quantum circuits execute up to 47 sequential $F$-moves. We identify idling errors as the dominant error source, which can be effectively mitigated using dynamical decoupling combined with a parallelized implementation of $F$-moves.
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https://arxiv.org/abs/2601.13530
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40d86bc0020e50d40d5a7face1a346fd5c1fecd5f9c88bc73e81bcc83005a5f9
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2026-01-21T00:00:00-05:00
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Kaleidoscope Yang-Baxter Equation for Gaudin's Kaleidoscope models
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arXiv:2601.13596v1 Announce Type: cross Abstract: Recently, researchers have proposed the Asymmetric Bethe ansatz method - a theoretical tool that extends the scope of Bethe ansatz-solvable models by "breaking" partial mirror symmetry via the introduction of a fully reflecting boundary. Within this framework, the integrability conditions which were originally put forward by Gaudin have been further generalized. In this work, building on Gaudin's generalized kaleidoscope model, we present a detailed investigation of the relationship between DN symmetry and its integrability. We demonstrate that the mathematical essence of integrability in this class of models is characterized by a newly proposed Kaleidoscope Yang-Baxter Equation. Furthermore, we show that the solvability of a model via the coordinate Bethe ansatz depends not only on the consistency relations satisfied by scattering matrices, but also on the model's boundary conditions and the symmetry of the subspace where solutions are sought. Through finite element method based numerical studies, we further confirm that Bethe ansatz integrability arises in a specific symmetry sector. Finally, by analyzing the algebraic structure of the Kaleidoscope Yang-Baxter Equation, we derive a series of novel quantum algebraic identities within the framework of quantum torus algebra.
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https://arxiv.org/abs/2601.13596
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5a9f5bcb241acbfc2fdd77e937c077dc0f308cc4192c0df60789eb56a9bd49e7
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2026-01-21T00:00:00-05:00
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Recent progress on disorder-induced topological phases
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arXiv:2601.13619v1 Announce Type: cross Abstract: Topological states of matter in disordered systems without translation symmetry have attracted great interest in recent years. These states with topological characters are not only robust against certain disorders, but also can be counterintuitively induced by disorders from a topologically trivial phase in the clean limit. In this review, we summarize the current theoretical and experimental progress on disorder-induced topological phases in both condensed-matter and artificial systems. We first introduce the topological Anderson insulators (TAIs) induced by random disorders and their topological characterizations and experimental realizations. We then discuss various extensions of TAIs with unique localization phenomena in quasiperiodic and non-Hermitian systems. We also review the theoretical and experimental studies on the disorder-induced topology in dynamical and many-body systems, including topological Anderson-Thouless pumps, disordered correlated topological insulators and average-symmetry protected topological orders acting as interacting TAI phases. Finally, we conclude the review by highlighting potential directions for future explorations.
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https://arxiv.org/abs/2601.13619
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9fbcc0938f9d8934d0137f4868364ce785fcd99b8b8d3356662a457fa8b3db3f
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2026-01-21T00:00:00-05:00
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Topological Anderson insulator and reentrant topological transitions in a mosaic trimer lattice
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arXiv:2601.13760v1 Announce Type: cross Abstract: We study the topological properties of a one-dimensional quasiperiodic-potential-modulated mosaic trimer lattice. To begin with, we first investigate the topological properties of the model in the clean limit free of quasiperiodic disorder based on analytical derivation and numerical calculations of the Zak phase $Z$ and the polarization $P$. Two nontrivial topological phases corresponding to the $1/3$ filling and $2/3$ filling, respectively, are revealed. Then we incorporate the mosaic modulation and investigate the influence of quasiperiodic disorder on the two existing topological phases. Interestingly, it turns out that quasiperiodic disorder gives rise to multiple distinct effects for different fillings. At $2/3$ filling, the topological phase is significantly enhanced by the quasiperiodic disorder and topological Anderson insulator emerges. Based on the calculations of polarization and energy gap, we explicitly present corresponding topological phase diagram in the $\lambda-J$ plane. While for the $1/3$ filling case, % the topological phase is dramatically suppressed by the same quasiperiodic disorder. the quasiperiodic disorder dramatically compresses the topological phase, and strikingly, further induces the emergence of reentrant topological phase transitions instead. Furthermore, we verify the topological phase diagrams by computing the many-body ground state fidelity susceptibility for both the $1/3$ filling and $2/3$ filling cases. Our work exemplifies the diverse roles of quasiperiodic disorder in the modulation of topological properties, and will further inspire more research on the competitive and cooperative interplay between topological properties and quasiperiodic disorder.
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https://arxiv.org/abs/2601.13760
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cd5566545ac7673edb6d6ab240f45f0f6809559bd2cad0d2f398fb2b7c0a46ee
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2026-01-21T00:00:00-05:00
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Quantum simulation of general spin-1/2 Hamiltonians with parity-violating fermionic Gaussian states
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arXiv:2601.13811v1 Announce Type: cross Abstract: We introduce equations of motion for a parity-violating fermionic mean-field theory (PV-FMFT): a numerically efficient fermionic mean-field theory based on parity-violating fermionic Gaussian states (PV-FGS). This work provides explicit equations of motion for studying the real- and imaginary-time evolution of spin-1/2 Hamiltonians with arbitrary geometries and interactions. We extend previous formulations of parity-preserving fermionic mean-field theory (PP-FMFT) by including fermionic displacement operators in the variational Ansatz. Unlike PP-FMFT, PV-FMFT can be applied to general spin-1/2 Hamiltonians, describe quenches from arbitrary initial spin-1/2 product states, and compute local and non-local observables in a straight-forward manner at the same modest computational cost as PP-FMFT -- scaling as $O(N^3)$ in the worst case for a system of $N$ spins or fermionic modes. We demonstrate that PV-FMFT can exactly capture the imaginary- and real-time dynamics of non-interacting spin-1/2 Hamiltonians. We then study the post quench-dynamics of the one- and two-dimensional Ising model in presence of longitudinal and transversal fields with PV-FMFT and compute the single site magnetization and correlation functions, and compare them against results from other state-of-the-art numerical approaches. In two-dimensional spin systems, we show that the employed spin-to-fermion mapping can break rotational symmetry within the PV-FMFT description, and we discuss the resulting consequences for the calculated correlation functions. Our work introduces PV-FMFT as a benchmark for other numerical techniques and quantum simulators, and it outlines both its capabilities and its limitations.
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https://arxiv.org/abs/2601.13811
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d39c1b0e0a9d6eda96a9d037452b698cfba077c0d889c774b40f3282944553f8
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2026-01-21T00:00:00-05:00
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Confinement-Induced Floquet Engineering and Non-Abelian Geometric Phases in Driven Quantum Wire Qubits
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arXiv:2601.13859v1 Announce Type: cross Abstract: This work theoretically demonstrates that a spin qubit in a parabolic quantum wire driven by a bichromatic field exhibits a confinement-tunable synthetic gauge field, leading to novel Floquet topological phenomena. The study presents the underlying mechanism for topological protection of qubit states against time-periodic perturbations. The analysis reveals a confinement-induced topological Landau-Zener transition, marked by a shift from preserved symmetries to chiral interference patterns in Landau-Zener-St$\ddot{u}$ckelberg-Majorana interferometry. Notably, the emergence of non-Abelian geometric phases under cyclic evolution in curved confinement and phase-parameter space is identified, enabling holonomic quantum computation. Additionally, the prediction of unconventional Floquet-Bloch oscillations in the quasi-energy and resonance transition probability spectra as a function of the biharmonic phase indicates exotic properties, including fractal spectra and fractional Floquet tunneling. These phenomena provide direct evidence of coherent transport in the synthetic dimension. Collectively, these findings position quantum wire materials has a versatile platform for Floquet engineering, topological quantum control, and fault-tolerant quantum information processing.
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https://arxiv.org/abs/2601.13859
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6a628aea8bdfd7a398fa639449129f7a9069797db983d3178e45b981a37a2cae
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2026-01-21T00:00:00-05:00
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To infinity and back -- $1/N$ graph expansions of light-matter systems
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arXiv:2601.13860v1 Announce Type: cross Abstract: We present a method for performing a full graph expansion for light-matter systems, utilizing the linked-cluster theorem. This method enables us to explore $1/N$ corrections to the thermodynamic limit $N\to \infty$ in the number of particles, giving us access to the mesoscopic regime. While this regime is yet largely unexplored due to the challenges of studying it with established approaches, it incorporates intriguing features, such as entanglement between light and matter that vanishes in the thermodynamic limit. As a representative application, we calculate physical quantities of the low-energy regime for the paradigmatic Dicke-Ising chain in the paramagnetic normal phase by accompanying the graph expansion with both exact diagonalization (NLCE) and perturbation theory (\pcst), benchmarking our approach against other techniques. We investigate the ground-state energy density and photon density, showing a smooth transition from the microscopic to the macroscopic regime up to the thermodynamic limit. Around the quantum critical point, we extract the $1/N$ corrections to the ground-state energy density to obtain the critical point and critical exponent using extrapolation techniques.
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https://arxiv.org/abs/2601.13860
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2d4fb28cd1f4e05975f2da1efff2d375e5da820ce2b124a2b907e41d56deb5e4
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2026-01-21T00:00:00-05:00
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The $O(n\to\infty)$ Rotor Model and the Quantum Spherical Model on Graphs
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arXiv:2601.14119v1 Announce Type: cross Abstract: We show that the large $n$ limit of the $O(n)$ quantum rotor model defined on a general graph has the same critical behavior as the corresponding quantum spherical model and that the critical exponents depend solely on the spectral dimension $d_s$ of the graph. To this end, we employ a classical to quantum mapping and use known results for the large $n$ limit of the classical $O(n)$ model on graphs. Away from the critical point, we discuss the interplay between the Laplacian and the Adjacency matrix in the whole parameter plane of the quantum Hamiltonian. These results allow us to paint the full picture of the $O(n)$ quantum rotor model on graphs in the large $n$ limit.
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https://arxiv.org/abs/2601.14119
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3e3ab38e58efc120038116bf10b4a39c2b5c541958e721111b2e1505b2c4d965
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2026-01-21T00:00:00-05:00
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Fundamental trade-off relation in probabilistic entanglement generation
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arXiv:2112.03233v3 Announce Type: replace Abstract: We investigate the generation of entanglement between two non-interacting systems by synthesizing a new quantum process from the superposition of distinct processes characterized by local-only operations. Our analysis leads to the derivation of a universal trade-off relation, $P_{\text{succ}}(1+\mathcal{C})\le1$, that fundamentally bounds the success probability ($P_{\text{succ}}$) and the generated entanglement (concurrence $\mathcal{C}$). The derivation of this trade-off relation is inspired by indefinite causal order, but applies for a broader class of quantum processes. Next, we show that the mathematical structure of this bound predicts the existence of a "quasi-deterministic" mode of operation, a surprising phenomenon which we then confirm with concrete entanglement generation protocols, where a maximally entangled state is guaranteed to be produced. In this mode of operation, both outcomes of the post-selection measurement on the auxiliary control system result in a maximally entangled state of the target system. Furthermore, we demonstrate how this general principle can be realized using a quantum switch, which leverages an indefinite causal order as a physical resource, and explore the rich variety of dynamical behaviors governed by the universal trade-off. Our results establish a general principle for entanglement generation with superposition of quantum processes and introduce a novel way of controlling entanglement generation.
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https://arxiv.org/abs/2112.03233
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a0f8931accd69d46d4cc005923825fefcfbe4dd0d0ee57c977f52bcb325ece0f
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2026-01-21T00:00:00-05:00
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Generalising Aumann's Agreement Theorem
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arXiv:2202.02156v3 Announce Type: replace Abstract: According to Aumann's celebrated theorem, rational agents cannot agree to disagree. In other words, agents who once shared a common prior probability distribution and who have common knowledge about their posteriors cannot assign different probability distributions to a given proposition. Common knowledge imposes strong restrictions on assigned probabilities. In fact, Aumann's agreement theorem was one of the first attempts to formalise and explore the role played by common knowledge in decision theory. Recently, the debate over possible (quantum) extensions of Aumann's results has resurfaced. This paper contributes to this discussion. First, we argue that agreeing to disagree is impossible in quantum theory. Secondly, by building on the quantum argument, we show that agreeing to disagree is also forbidden in any generalised probability theory. The upshot is that in its probabilistic version, the agreement theorem is a direct consequence of how we choose to condition upon acquiring new information.
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https://arxiv.org/abs/2202.02156
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99f31044e5b87e256c35766b828faf7c13d547c047303e9d5671a3663559f663
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2026-01-21T00:00:00-05:00
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Establishing trust in quantum computations
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arXiv:2204.07568v2 Announce Type: replace Abstract: Quantum computing hardware has grown sufficiently complex that it often can no longer be simulated by classical computers, but its computational power remains limited by errors. These errors corrupt the results of quantum algorithms, and it is no longer always feasible to use classical simulations to directly check the correctness of quantum computations. Without practical methods for quantifying the accuracy with which a quantum algorithm has been executed, it is difficult to establish trust in the results of a quantum computation. Here we solve this problem, by introducing a simple and efficient technique for measuring the fidelity with which an as-built quantum computer can execute an algorithm. Our technique converts the algorithm's quantum circuits into a set of closely related ``mirror circuits'' whose success rates can be efficiently measured. It enables measuring the fidelity of quantum algorithm executions both in the near-term, with algorithms run on hundreds or thousands of physical qubits, and into the future, with algorithms run on logical qubits protected by quantum error correction.
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https://arxiv.org/abs/2204.07568
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3722ad16b22d3ac00d8dde0c6a4520f6b99693e027e2ba51902c96081b1d5771
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2026-01-21T00:00:00-05:00
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Nonadiabatic transitions in non-Hermitian $\mathcal{PT}$-symmetric two-level systems
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arXiv:2301.10382v3 Announce Type: replace Abstract: We systematically characterize the dynamical evolution of time-parity (PT )-symmetric two-level systems with spin-dependent dissipations. If the control parameters of the gap are linearly tuned with time, the dynamical evolution can be characterized with parabolic cylinder equations which can be analytically solved. We find that the asymptotic behaviors of particle probability on the two levels show initial-state-independent redistribution in the slow-tuning-speed limit as long as the system is nonadiabatically driven across exceptional points. Equal distributions appear when the nondissipative Hamiltonian shows gap closing. So long as the nondissipative Hamiltonian displays level anticrossing, the final distribution becomes unbalanced. The ratios between the occupation probabilities are given analytically. These results are confirmed with numerical simulations. The predicted equal distribution phenomenon may be used to identify the closing of the energy gap from anti-crossing between two energy bands.
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https://arxiv.org/abs/2301.10382
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5925a8c014d94c7bbd9c0bf75b3b5b2b45625ee059a40e9cd69c2801c56f3397
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2026-01-21T00:00:00-05:00
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Spectral Gaps via Imaginary Time
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arXiv:2303.02124v2 Announce Type: replace Abstract: The spectral gap occupies a role of central importance in many open problems in physics. We present an approach for evaluating the spectral gap of a Hamiltonian from a simple ratio of two expectation values, both of which are evaluated using a quantum state that is evolved in imaginary time. In principle, the only requirement is that the initial state is supported on both the ground and first excited states. We demonstrate this approach for the Fermi-Hubbard and transverse-field Ising models through numerical simulation. We then go on to explore avenues for its implementation on quantum computers using imaginary-time quantum dynamical emulation.
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https://arxiv.org/abs/2303.02124
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5a037d9b8a1f4862ac8e4223ca5672a7340e2241976e69b26f473f5c9fb2c45a
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2026-01-21T00:00:00-05:00
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A Computational Tsirelson's Theorem for the Value of Compiled XOR Games
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arXiv:2402.17301v3 Announce Type: replace Abstract: Nonlocal games are a foundational tool for understanding entanglement and constructing quantum protocols in settings with multiple spatially separated quantum devices. In this work, we continue the study initiated by Kalai et al. (STOC '23) of compiled nonlocal games, played between a classical verifier and a single cryptographically limited quantum device. Our main result is that the compiler proposed by Kalai et al. is sound for any two-player XOR game. A celebrated theorem of Tsirelson shows that for XOR games, the quantum value is exactly given by a semidefinite program, and we obtain our result by showing that the SDP upper bound holds for the compiled game up to a negligible error arising from the compilation. This answers a question raised by Natarajan and Zhang (FOCS '23), who showed soundness for the specific case of the CHSH game. Using our techniques, we obtain several additional results, including (1) tight bounds on the compiled value of parallel-repeated XOR games, (2) operator self-testing statements for any compiled XOR game, and (3) a ``nice'' sum-of-squares certificate for any XOR game, from which operator rigidity is manifest.
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https://arxiv.org/abs/2402.17301
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f49c49096cc2f4e00c57cbdff7e8184d3d802a34a4003e983ade934761356d36
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2026-01-21T00:00:00-05:00
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Feedback-Based Quantum Algorithm for Excited States Calculation
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arXiv:2404.04620v2 Announce Type: replace Abstract: Recently, feedback-based quantum algorithms have been introduced to calculate the ground states of Hamiltonians, inspired by quantum Lyapunov control theory. This paper aims to generalize these algorithms to the problem of calculating an eigenstate of a given Hamiltonian, assuming that the lower energy eigenstates are known. To this aim, we propose a new design methodology that combines the layer-wise construction of the quantum circuit in feedback-based quantum algorithms with a new feedback law based on a new Lyapunov function to assign the quantum circuit parameters. We present two approaches for evaluating the circuit parameters: one based on the expectation and overlap estimation of the terms in the feedback law and another based on the gradient of the Lyapunov function. We demonstrate the algorithm through an illustrative example and through an application in quantum chemistry. To assess its performance, we conduct numerical simulations and execution on IBM's superconducting quantum computer.
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https://arxiv.org/abs/2404.04620
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d30d365438612e6e2129f9c9cabc2e65a72138e267cdcfb2a970d03c9e16c9df
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2026-01-21T00:00:00-05:00
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Improving the trainability of VQE on NISQ computers for solving portfolio optimization using convex interpolation
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arXiv:2407.05589v3 Announce Type: replace Abstract: Solving combinatorial optimization problems using variational quantum algorithms (VQAs) might be a promise application in the NISQ era. However, the limited trainability of VQAs could hinder their scalability to large problem sizes. In this paper, we improve the trainability of variational quantum eigensolver (VQE) by utilizing convex interpolation to solve portfolio optimization. Based on convex interpolation, the location of the ground state can be evaluated by learning the property of a small subset of basis states in the Hilbert space. This enlightens naturally the proposals of the strategies of close-to-solution initialization, regular cost function landscape, and recursive ansatz equilibrium partition. The successfully implementation of a $40$-qubit experiment using only $10$ superconducting qubits demonstrates the effectiveness of our proposals. Furthermore, the quantum inspiration has also spurred the development of a prototype greedy algorithm. Extensive numerical simulations indicate that the hybridization of VQE and greedy algorithms achieves a mutual complementarity, combining the advantages of both global and local optimization methods. Our proposals can be extended to improve the trainability for solving other large-scale combinatorial optimization problems that are widely used in real applications, paving the way to unleash quantum advantages of NISQ computers in the near future.
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https://arxiv.org/abs/2407.05589
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141f36007ace0c9b1ca31fa41a88196ea6abb27bca589da8a8b475344b573779
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2026-01-21T00:00:00-05:00
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Discretized Quantum Exhaustive Search for Variational Quantum Algorithms
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arXiv:2407.17659v2 Announce Type: replace Abstract: Quantum computers promise a great computational advantage over classical computers, yet currently available quantum devices have only a limited amount of qubits and a high level of noise, limiting the size of problems that can be solved accurately with those devices. Variational Quantum Algorithms (VQAs) have emerged as a leading strategy to address these limitations by optimizing cost functions based on measurement results of shallow-depth circuits. However, the optimization process usually suffers from severe trainability issues as a result of the exponentially large search space, mainly local minima and barren plateaus. Here we propose a novel method that can improve variational quantum algorithms -- ``discretized quantum exhaustive search''. On classical computers, exhaustive search, also named brute force, solves small-size NP complete and NP hard problems. Exhaustive search and efficient partial exhaustive search help designing heuristics and exact algorithms for solving larger-size problems by finding easy subcases or good approximations. We adopt this method to the quantum domain, by relying on mutually unbiased bases for the $2^n$-dimensional Hilbert space. We define a discretized quantum exhaustive search that works well for small size problems. We provide an example of an efficient partial discretized quantum exhaustive search for larger-size problems, in order to extend classical tools to the quantum computing domain, for near future and far future goals. Our method enables obtaining intuition on NP-complete and NP-hard problems as well as on Quantum Merlin Arthur (QMA)-complete and QMA-hard problems. We demonstrate our ideas in many simple cases, providing the energy landscape for various problems and presenting two types of energy curves via VQAs.
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https://arxiv.org/abs/2407.17659
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444e4d183817e89fae9c99c4d37f69a42642470ed3c63afecb766aebbe4e02d0
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2026-01-21T00:00:00-05:00
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Time Derivatives of Weak Values
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arXiv:2409.01460v4 Announce Type: replace Abstract: The time derivative of a physical property often gives rise to another meaningful property. Since weak values provide empirical insights that cannot be derived from expectation values, this paper explores what physical properties can be obtained from the time derivative of weak values. It demonstrates that, in general, the time derivative of a gauge-invariant weak value is neither a weak value nor a gauge-invariant quantity. Two conditions are presented to ensure that the left- or right-time derivative of a weak value is also a gauge-invariant weak value. Under these conditions, a local Ehrenfest-like theorem can be derived for weak values giving a natural interpretation for the time derivative of weak values. Notably, a single measured weak value of the system's position provides information about two additional unmeasured weak values: the system's local velocity and acceleration, through the first- and second-order time derivatives of the initial weak value, respectively. These findings also offer guidelines for experimentalists to translate the weak value theory into practical laboratory setups, paving the way for innovative quantum technologies. An example illustrates how the electromagnetic field can be determined at specific positions and times from the first- and second-order time derivatives of a weak value of position.
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https://arxiv.org/abs/2409.01460
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b00a6294f151ad8aafe614465b5d8bd7f1dd66daba2b83ac92f54b54e288c48e
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2026-01-21T00:00:00-05:00
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A Geometric Substructure for Quantum Dynamics
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arXiv:2411.08230v5 Announce Type: replace Abstract: The description of a closed quantum system is extended with the identification of an underlying substructure enabling an expanded formulation of dynamics in the Heisenberg picture. Between measurements a ``state point" moves in an underlying multi-dimensional complex projective space with constant velocity determined by the quantum state vector. Following a measurement the point changes direction and moves with new constant velocity along one of several possible new orthogonal paths with probabilities determined by the Born Interpretation of the state vector. From this previously hidden substructure a new picture of quantum dynamics and quantum measurements emerges without violating existing no-gotheorems regarding hidden variables. A natural generalisation to a Riemannian substructure is proposed, determined by the entropy of the background environment. This leads to a suggestedinteraction between the substructure of quantum dynamics and the background gravitational field.
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https://arxiv.org/abs/2411.08230
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1a695331f78947ef848fc391b67ad363c54aa1249f6ecdd48f91d8720e6ef8c5
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2026-01-21T00:00:00-05:00
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Restricted Monte Carlo wave function method and Lindblad equation for identifying entangling open-quantum-system dynamics
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arXiv:2412.08735v2 Announce Type: replace Abstract: We develop an extension of the Monte Carlo wave function approach that unambiguously identifies dynamical entanglement in general composite, open systems. Our algorithm performs tangential projections onto the set of separable states, leading to classically correlated quantum trajectories. By comparing this restricted evolution with the unrestricted one, we can characterize the entangling capabilities of quantum channels without making use of input-output relations. Moreover, applying this method is equivalent to solving the nonlinear master equation in Lindblad form introduced in \cite{PAH24} for two-qubit systems. We here extend these equations to multipartite systems of qudits, describing non-entangling dynamics in terms of a stochastic differential equation. We identify the impact of dynamical entanglement in open systems by applying our approach to several correlated decay processes. Therefore, our methodology provides a complete and ready-to-use framework to characterize dynamical quantum correlations caused by arbitrary open-system processes.
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https://arxiv.org/abs/2412.08735
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9f52c8e5e1731256a845fcced82151826b01ac1d3400ea46ad25b8d049d5ad71
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2026-01-21T00:00:00-05:00
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Optimal Hamiltonian recognition of unknown quantum dynamics
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arXiv:2412.13067v2 Announce Type: replace Abstract: Identifying unknown Hamiltonians from their quantum dynamics is a pivotal challenge in quantum technologies. In this paper, we introduce Hamiltonian recognition, a framework that bridges quantum hypothesis testing and quantum metrology, aiming to identify the Hamiltonian governing quantum dynamics from a known set of Hamiltonians. To identify $H$ for an unknown qubit quantum evolution $\exp(-iH\theta)$ with unknown $\theta$, from two or three orthogonal Hamiltonians, we develop a quantum algorithm for coherent function simulation, built on two quantum signal processing (QSP) structures. It can simultaneously realize a target polynomial based on measurement results regardless of the chosen signal unitary for the QSP. Utilizing semidefinite optimization and group representation theory, we prove that our methods achieve the optimal average success probability, taken over possible Hamiltonians $H$ and parameters $\theta$, decays as $O(1/k)$ with $k$ queries of the unknown unitary transformation. Furthermore, we demonstrate the validity of our protocol on a superconducting quantum processor. We also investigate a physically motivated recognition task for Heisenberg Hamiltonians, providing numerical evidence for effective multi-qubit quantum system recognition. This work presents an efficient method to recognize Hamiltonians from limited queries of the dynamics, opening new avenues in composite channel discrimination and quantum metrology.
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https://arxiv.org/abs/2412.13067
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b1dbbd0e90800be40f9252db1a64746307eff1ed22567de80793a55e59d10a4d
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2026-01-21T00:00:00-05:00
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Characterisation of individual gates using twirling circuits
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arXiv:2412.15466v2 Announce Type: replace Abstract: We present a method to characterise qubit gates. Utilising the supermap formalism, we create a scheme for deterministic single-qubit gate analysis. Our approach introduces a new twirling process that is applied directly through fixed circuits. This method removes the requirement to average over random gates. The results enhance randomised benchmarking techniques and are suitable for experimental setups with multi-qubit control, focusing on the precise characterisation of single-qubit gates.
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https://arxiv.org/abs/2412.15466
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2f134856803412e48f0b6f0f34d756a129fa7b021550b85a4596f0c681a7a120
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2026-01-21T00:00:00-05:00
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Dissipating quartets of excitations in a superconducting circuit
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arXiv:2501.05960v3 Announce Type: replace Abstract: Over the past decade, autonomous stabilization of bosonic qubits has emerged as a promising approach for hardware-efficient protection of quantum information. However, applying these techniques to more complex encodings than the Schr\"odinger cat code requires exquisite control of high-order wave mixing processes. The challenge is to enable specific multiphotonic dissipation channels while avoiding unintended non-linear interactions. In this work, we leverage a genuine six-wave mixing process enabled by a near Kerr-free Josephson element to enforce dissipation of quartets of excitations in a high-impedance superconducting resonator. Owing to residual non-linearities stemming from stray inductances in our circuit, this dissipation channel is only effective when the resonator holds a specific number of photons. Applying it to the fourth excited state of the resonator, we show an order of magnitude enhancement of the state decay rate while only marginally impacting the relaxation and coherence of lower energy states. Given that stray inductances could be strongly reduced through simple modifications in circuit design and that our methods can be adapted to activate even higher-order dissipation channels, these results pave the way toward the dynamical stabilization of four-component Schr\"odinger cat qubits and even more complex bosonic qubits.
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https://arxiv.org/abs/2501.05960
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2026-01-21T00:00:00-05:00
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QSteed: A Resource-Virtualized and Hardware-Aware Quantum Compilation Framework for Real Quantum Computing Processors
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arXiv:2501.06993v2 Announce Type: replace Abstract: As quantum computing systems continue to scale up and become more clustered, efficiently compiling user quantum programs into high fidelity executable sequences on real hardware remains a key challenge for current quantum compilation systems. In this study, we introduce a system software framework that integrates resource virtualization and hardware aware compilation for real quantum computing processors, termed QSteed. QSteed virtualizes quantum processors through a four layer abstraction hierarchy comprising the Real Quantum Processing Unit (QPU), Standard QPU (StdQPU), Substructure of the QPU (SubQPU), and Virtual QPU (VQPU). These abstractions, together with calibration data, device topology, and noise descriptors, are maintained in a dedicated database to enable unified and fine grained management across superconducting quantum platforms. At run time, the modular compiler queries the database to match each incoming circuit with the most suitable VQPU, after which it confines layout, routing, gate resynthesis, and noise adaptive optimizations to that virtual subregion. The complete stack has been deployed on the Quafu superconducting cluster, where experimental runs confirm the correctness of the virtualization model and the efficacy of the compiler without requiring modifications to user code. By integrating resource virtualization with a select-then-compile workflow, QSteed demonstrates a robust architecture for compiling programs on noisy superconducting processors. This architectural approach offers a promising path towards efficient compilation needs across various superconducting quantum computing platforms in the noisy intermediate scale quantum (NISQ) era.
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https://arxiv.org/abs/2501.06993
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f999c005e3fe180cebb282583eb088421908e885af3bc3f458478a4966e00566
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2026-01-21T00:00:00-05:00
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Unifying quantum stochastic methods using Wick's theorem on the Keldysh contour
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arXiv:2501.09544v2 Announce Type: replace Abstract: We present a method, based on the Keldysh formalism, for deriving stochastic master equations that describe the non-Markovian dynamics of a quantum system coupled to a Gaussian environment. This approach yields a compact expression for the system's propagator, which we show to be equivalent to existing formulations, such as the stochastic von Neumann equation (SVNE). A key advantage of our method is its generality: It can be extended to describe any open-system evolution defined on a suitable ordering contour. As a result, we adapt it to derive generalized versions of the SVNE that account for initial system-environment correlations, as well as stochastic equations that incorporate information about the statistics of energy flows in the environment. The insights offered by our technique further allow us to examine the nature of the noise processes appearing in the SVNE. We prove that its solution can be expressed in terms of a single physical noise, without any loss of information. Finally, we propose a semiclassical scenario in which this noise can be interpreted as arising from an initial measurement process on the environment.
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https://arxiv.org/abs/2501.09544
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6fd3e173e628d9249957269a980762ed06c6586046a3df8a31087413302f4488
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2026-01-21T00:00:00-05:00
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On the distinguishability of geometrically uniform quantum states
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arXiv:2501.12376v2 Announce Type: replace Abstract: A geometrically uniform (GU) ensemble is a uniformly weighted quantum state ensemble generated from a fixed state by a unitary representation of a finite group $G$. In this work we analyze the problem of discriminating GU ensembles from various angles. Assuming that the representation of $G$ is irreducible, we first show that a particular optimal measurement can be understood as the limit of weighted `pretty good measurements' (PGM). This naturally provides examples of state discrimination for which the unweighted PGM is provably sub-optimal. We extend this analysis to certain reducible representations, and use Schur-Weyl duality to discuss two particular examples of GU ensembles in terms of Werner-type and permutation-invariant generator states. For the case of pure-state GU ensembles we give a streamlined proof of optimality of the PGM first proved in [Eldar et al., 2004]. We use this result to give simplified proofs of the optimality of the PGM, along with expressions for the corresponding success probabilities, for two tasks: the hidden subgroup problem over semidirect product groups (first proved in [Bacon et al., 2005]), and port-based teleportation (first proved in [Mozrzymas et al., 2019] and [Leditzky, 2022]). Finally, we consider the $n$-copy setting and adapt a result of [Montanaro, 2007] to derive a compact and easily evaluated lower bound on the success probability of the PGM for this task. This result can be applied to the hidden subgroup problem to obtain a new proof for an upper bound on the sample complexity by [Hayashi et al., 2006].
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https://arxiv.org/abs/2501.12376
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fb5907660667b5a985f095c343e399201064ba1e64df10c027d04498b6c1f363
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2026-01-21T00:00:00-05:00
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Exact non-Markovian master equations: a generalized derivation for Gaussian systems
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arXiv:2502.14364v3 Announce Type: replace Abstract: We derive an exact master equation that captures the dynamics of a quadratic quantum system linearly coupled to a Gaussian environment of the same statistics: the Gaussian Master Equation (GME). Unlike previous approaches, our formulation applies universally to both bosonic and fermionic setups, and remains valid even in the presence of initial system-environment correlations, allowing for the exact computation of the system's reduced density matrix across all parameter regimes. Remarkably, the GME shares the same operatorial structure as the Redfield equation and depends on a single kernel - a dressed environment correlation function accounting for all virtual interactions between the system and the environment. This simple structure grants a clear physical interpretation and makes the GME easy to simulate numerically, as we show by applying it to an open system based on two fermions coupled via superconductive pairing.
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https://arxiv.org/abs/2502.14364
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2026-01-21T00:00:00-05:00
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Quantum state exclusion for group-generated ensembles of pure states
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arXiv:2503.02568v2 Announce Type: replace Abstract: Quantum state exclusion is the task of determining which states from a given set a system was not prepared in. We provide a complete solution to optimal quantum state exclusion for arbitrary sets of pure states generated by finite groups, establishing necessary and sufficient conditions for perfect (zero-error conclusive) exclusion. When perfect exclusion is impossible, we introduce two natural extensions: minimum-error and unambiguous exclusion. For both, we derive the optimal protocols and present analytical expressions for the corresponding failure probabilities and measurements, providing additional insight into how quantum states encode information.
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https://arxiv.org/abs/2503.02568
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c073e5dc76cdd27bdf12b5132e73fa5eab8ccbcfc0fc2d0e0fc543992dc81374
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2026-01-21T00:00:00-05:00
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Scalable quantum simulator with an extended gate set in giant atoms
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arXiv:2503.04537v3 Announce Type: replace Abstract: Quantum computation and quantum simulation require a versatile gate set to optimize circuit compilation for practical applications. However, existing platforms are often limited to specific gate types or rely on parametric couplers to extend their gate set, which compromises scalability. Here, we propose a scalable quantum simulator with an extended gate set based on giant-atom three-level systems, which can be implemented with superconducting circuits. Unlike conventional small atoms, giant atoms couple to the environment at multiple points, introducing interference effects that allow exceptional tunability of their interactions. By leveraging this tunability, our setup supports both CZ and iSWAP gates through simple frequency adjustments, eliminating the need for parametric couplers. This dual-gate capability enhances circuit efficiency, reducing the overhead for quantum simulation. As a demonstration, we showcase the simulation of spin dynamics in dissipative Heisenberg XXZ spin chains, highlighting the setup's ability to tackle complex open quantum many-body dynamics. Finally, we discuss how a two-dimensional extension of our system could enable fault-tolerant quantum computation, paving the way for a universal quantum processor.
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https://arxiv.org/abs/2503.04537
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4ef9a1d850de3d2859a410920b5a0e7fa2f70d35ee92c77de63a051b8413e051
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2026-01-21T00:00:00-05:00
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A Multilevel Framework for Partitioning Quantum Circuits
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arXiv:2503.19082v4 Announce Type: replace Abstract: Executing quantum algorithms over distributed quantum systems requires quantum circuits to be divided into sub-circuits which communicate via entanglement-based teleportation. Naively mapping circuits to qubits over multiple quantum processing units (QPUs) results in large communication overhead, increasing both execution time and noise. This can be minimised by optimising the assignment of qubits to QPUs and the methods used for covering non-local operations. Formulations that are general enough to capture the spectrum of teleportation possibilities lead to complex problem instances which can be difficult to solve effectively. This highlights a need to exploit the wide range of heuristic techniques used in the graph partitioning literature. This paper formalises and extends existing constructions for graphical quantum circuit partitioning and designs a new objective function that captures further possibilities for non-local operations via nested state teleportation. We adapt the well-known Fiduccia-Mattheyses heuristic to the constraints and problem objective and explore multilevel techniques that coarsen hypergraphs and partition at multiple levels of granularity. We find that this reduces runtime and improves solution quality of standard partitioning. We place these techniques within a larger framework, through which we can extract full distributed quantum circuits including teleportation instructions. We compare the entanglement requirements and runtimes with state-of-the-art methods, finding that we achieve the lowest entanglement costs in most cases. Averaging over a wide range of circuits, we reduce the entanglement requirements by 35% compared with the next best-performing method. We also find that our techniques can scale to much larger circuit sizes than competing methods, provided the number of partitions is not too large.
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https://arxiv.org/abs/2503.19082
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bd3fbe38051e1905bcb1abc49340569748185a2a1c83d7972c785cde2ad87744
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2026-01-21T00:00:00-05:00
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Dissipation and non-thermal states in cryogenic cavities
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arXiv:2504.00591v3 Announce Type: replace Abstract: We study the properties of photons in a cryogenic cavity, made by cryo-cooled mirrors surrounded by a room temperature environment. We model such a system as a multimode cavity coupled to two thermal reservoirs at different temperatures. Using a Lindblad master equation approach, we derive the photon distribution and the statistical properties of the cavity modes, finding an overall non-thermal state described by a mode-dependent effective temperature. We also calculate the dissipation rates arising from the interaction of the cavity field with the external environment and the mirrors, relating such rates to measurable macroscopic quantities. These results provide a simple theory to calculate the dissipative properties and the effective temperature of a cavity coupled to different thermal reservoirs, offering potential pathways for engineering dissipations and photon statistics in cavity settings.
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https://arxiv.org/abs/2504.00591
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db40f539764965a7159c1beb266f64088f716eb701db111ae6a3e7dc016755f6
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2026-01-21T00:00:00-05:00
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Dynamically stable two-mode squeezing in cavity optomechanics
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arXiv:2504.03247v5 Announce Type: replace Abstract: Bosonic two-mode squeezed states are paradigmatic entangled states with broad applications in quantum information processing and quantum metrology. In this work, we propose a two-mode squeezing scheme in a hybrid three-mode cavity optomechanical system, where a mechanical resonator couples to two microwave (or optical) photon modes. By applying and modulating strong driving pulses to the photon modes, we construct an effective Hamiltonian that describes two-photon squeezing mediated by the mechanical mode. This effective Hamiltonian is validated through diagonalization of the full system's transition matrix in the Heisenberg picture. With the effective Hamiltonian, we provide a rigorous theoretical solution for the dynamical process of squeezing generation within the framework of open quantum system. Our analysis reveals that stable two-mode squeezing can be obtained by optimizing the squeezing quadrature operator, even in unsteady system states. Remarkably, the squeezing level can exceed the maximum achievable under system stability conditions. Furthermore, we show that our protocol is robust against systematic errors in both driving intensity and frequency, as well as against thermal Markovian noises. Our work provides an extendable approach for generating two-mode squeezed states between indirectly coupled Gaussian modes.
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https://arxiv.org/abs/2504.03247
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4cf9f2cf4cb50a0a2ddd0789848dd9d204712280ed22ac84c1091e45b6951435
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2026-01-21T00:00:00-05:00
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Fault-tolerant protocols through spacetime concatenation
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arXiv:2504.08918v4 Announce Type: replace Abstract: We introduce a framework called spacetime concatenation for fault-tolerant compilation of syndrome extraction circuits of stabilizer codes. Spacetime concatenation enables efficient compilation of syndrome extraction circuits into dynamical codes through structured gadget layouts and encoding matrices, facilitating low-weight measurements while preserving logical information. Our framework uses conditions that are sufficient for fault-tolerance of the dynamical code, including not measuring logical operators and preserving the spacetime distance. We construct explicit examples of dynamical codes using this framework, including the dynamical bivariate bicycle code and a dynamical Haah code, while illustrating their fault-tolerant properties. Furthermore, we analyze the classification and resource trade-offs of dynamical codes, demonstrating their adaptability to hardware constraints, including fabrication defects and qubit dropout scenarios.
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https://arxiv.org/abs/2504.08918
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fc01f32df258cab35c824710310bdc2cd8e63bbc582efbee41a4a2dcd4aa4379
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2026-01-21T00:00:00-05:00
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Micromagnons and long-range entanglement in ferrimagnetic ground states
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arXiv:2504.18724v2 Announce Type: replace Abstract: While significant attention has been devoted to studying entanglement in photonic systems, solid-state spin lattices remain relatively underexplored. Motivated by this gap, we investigate the entanglement structure of one-dimensional ferrimagnetic chains composed of alternating spin-1/2 and spin-3/2 particles. We characterize the ground-state correlations using exact diagonalization and the Density Matrix Renormalization Group method. Although the bipartite entanglement is restricted to nearest neighbors, we reveal the presence of long-range genuine multipartite entanglement between spatially separated spin pairs. These findings advance our understanding of quantum correlations in ferrimagnetic materials. The micromagnon description allows to provide fast approximation of ground states of ferrimagnets and emphasizes presence of multipartite correlations not widely discussed thus far.
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https://arxiv.org/abs/2504.18724
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d097fede156f6898091e0d0e1a8ea29479211be2d508f252abc4763ecc9ca663
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2026-01-21T00:00:00-05:00
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High-Temperature Fermionic Gibbs States are Mixtures of Gaussian States
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arXiv:2505.09730v2 Announce Type: replace Abstract: Efficient simulation of a quantum system generally relies on structural properties of the quantum state. Motivated by the recent results by Bakshi et al. on the sudden death of entanglement in high-temperature Gibbs states of quantum spin systems, we study the high-temperature Gibbs states of bounded-degree local fermionic Hamiltonians, which include the special case of geometrically local fermionic systems. We prove that at a sufficiently high temperature that is independent of the system size, the Gibbs state is a probabilistic mixture of fermionic Gaussian states. This forms the basis of an efficient classical algorithm to prepare the Gibbs state by sampling from a distribution of fermionic Gaussian states. As a contrasting example, we show that high-temperature Gibbs states of the Sachdev-Ye-Kitaev (SYK) model are not convex mixtures of Gaussian states.
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https://arxiv.org/abs/2505.09730
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6604c7af5b1e4f0a2e376401d3617368d01afda3aabaa6a470e9834bbc8356b0
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2026-01-21T00:00:00-05:00
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Experimental robustness benchmarking of quantum neural networks on a superconducting quantum processor
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arXiv:2505.16714v2 Announce Type: replace Abstract: Quantum machine learning (QML) models, like their classical counterparts, are vulnerable to adversarial attacks, hindering their secure deployment. Here, we report the first systematic experimental robustness benchmark for 20-qubit quantum neural network (QNN) classifiers executed on a superconducting processor. Our benchmarking framework features an efficient adversarial attack algorithm designed for QNNs, enabling quantitative characterization of adversarial robustness and robustness bounds. From our analysis, we verify that adversarial training reduces sensitivity to targeted perturbations by regularizing input gradients, significantly enhancing QNN's robustness. Additionally, our analysis reveals that QNNs exhibit superior adversarial robustness compared to classical neural networks, an advantage attributed to inherent quantum noise. Furthermore, the empirical upper bound extracted from our attack experiments shows a minimal deviation ($3 \times 10^{-3}$) from the theoretical lower bound, providing strong experimental confirmation of the attack's effectiveness and the tightness of fidelity-based robustness bounds. This work establishes a critical experimental framework for assessing and improving quantum adversarial robustness, paving the way for secure and reliable QML applications.
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https://arxiv.org/abs/2505.16714
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e044d7c90367e25b4f638ba8ee826ac29879e63d58ad7e0a5ff0802eb72b5b53
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2026-01-21T00:00:00-05:00
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Probing the quantum motion of a macroscopic mechanical oscillator with a radio-frequency superconducting qubit
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arXiv:2505.21481v2 Announce Type: replace Abstract: Long-lived mechanical resonators like drums oscillating at MHz frequencies and operating in the quantum regime are a powerful platform for quantum technologies and tests of fundamental physics. Yet, quantum control of such systems remains challenging, owing to their low energy scale and the difficulty of achieving efficient coupling to other well-controlled quantum devices. Here, we demonstrate repeated coherent interactions between a 4 MHz suspended silicon nitride membrane and a resonant superconducting heavy-fluxonium qubit. The qubit is initialized at an effective temperature of $21~\mathrm{\mu K}$ and read out with 77% single-shot fidelity. During the $6~\mathrm{ms}$ lifetime of the membrane the two systems swap excitations more than 300 times. After each interaction, a state-selective qubit detection is performed, implementing a stroboscopic series of weak measurements that provide information about the mechanical state. The accumulated records reconstruct the position noise spectrum of the membrane, revealing both its thermal occupation $n_\mathrm{th}\approx47$ at $10~\mathrm{mK}$ and the qubit-induced back-action. By preparing the qubit either in its ground or excited state before each interaction, we observe an imbalance between the emission and absorption spectra, proportional to $n_\mathrm{th}$ and $n_\mathrm{th}+1$, respectively-a hallmark of the non-commutation of phonon creation and annihilation operators. Since the predicted Di\'osi-Penrose gravitational collapse time is comparable to the measured mechanical decoherence time, our architecture enters a regime where gravity-induced decoherence could be tested directly.
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https://arxiv.org/abs/2505.21481
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55cecf20fb52fd7023069426a5e929a79b9dac845a4e7b48cc5c225588fe975c
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2026-01-21T00:00:00-05:00
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Generalized momentum operators from Fourier transform correspondence
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arXiv:2506.10950v2 Announce Type: replace Abstract: In this work we take a closer look at the algebraic-operator correspondence between the momentum space and the position space which defines the form of the canonical momentum operator in position space in Quantum Mechanics (QM). Starting from the Fourier transform (FT) relationship, we present a Hermitian generalization of the canonical momentum operator in position space. The action of the generalized operator is found to generate a local flow accompanied by position-dependent rescaling, rather than a global translation. Explicit eigenfunctions are obtained for representative cases and are shown to possess a well-defined limit to the plane-wave solution in QM. As an illustration, the infinite square well problem is solved using the generalized operator, yielding a deformed spectrum that has a smooth limit to the standard QM result.
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https://arxiv.org/abs/2506.10950
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45deed0b966b507d6745a7d37f36decf9be42fffbbb3e1c03133fcb2bdbdf3dc
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2026-01-21T00:00:00-05:00
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Learning quantum tomography from incomplete measurements
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arXiv:2506.19428v4 Announce Type: replace Abstract: We revisit quantum tomography in an informationally incomplete scenario and propose improved state reconstruction methods using deep neural networks. In the first approach, the trained network predicts an optimal linear or quadratic reconstructor with coefficients depending only on the collection of (already taken) measurement operators. This effectively refines the undercomplete tomographic reconstructor based on pseudoinverse operation. The second, based on an LSTM recurrent network performs state reconstruction sequentially. It can also optimize the measurement sequence, which suggests a no-free-lunch theorem for tomography: by narrowing the state space, we gain the possibility of more efficient tomography by learning the optimal sequence of measurements. Numerical experiments for a 2-qubit system show that both methods outperform standard maximum likelihood estimation and also scale to larger 3- and 4-qubit systems. Our results demonstrate that neural networks can effectively learn the underlying geometry of multi-qubit states using this for their reconstruction.
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https://arxiv.org/abs/2506.19428
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e721220d918daad2f7b503ed6c3e9c7ab15d71d2ea0a3500dc87a2d3e11db771
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2026-01-21T00:00:00-05:00
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Free Electron Paths from Dirac's Wave Equation Elucidating Zitterbewegung and Spin
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arXiv:2506.20857v3 Announce Type: replace Abstract: The worldline of a free electron is revealed by applying Dirac's velocity operator to its Dirac wave function whose space-time arguments are expressed in a proper time by a Lorentz transformation. This motion can be decomposed into two parts: the electron's global motion of its inertia (or spin) center and an inherent local periodic motion about this point that produces the electron's spin and has the zitterbewegung frequency found by Schr\"{o}dinger in his operator analysis of Dirac's wave equation. This zitter motion corresponds to the so-called polarization and magnetization currents in Gordon's decomposition of Dirac's current. In an inertial "rest"-frame fixed at the inertia center, Dirac's wave function for a free electron with its spin in a specified direction implies that the zitter motion is a perpetual circular motion about the inertia center in a plane orthogonal to this spin direction with a radius one half of the Compton radius and moving at the speed of light. The electron continuously accelerates about the spin center without any external force because the inertia is effective at the spin center, rather than at its charge center where the electron interacts with the electro-magnetic field. This analysis confirms the nature of zitterbewegung directly from Dirac's wave equation, agreeing with the conclusions of Barut and Zanghi, Beck, Hestenes, Rivas and Salesi from their classical Dirac particle models of the electron. Furthermore, these five classical models are equivalent and express the same free electron dynamics as Dirac's equation.
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https://arxiv.org/abs/2506.20857
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8933ad0c3a917e6accb10270742676724506087fb1ca928bf9d159bd3744376e
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2026-01-21T00:00:00-05:00
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Topologically noise robust network steering without inputs
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arXiv:2506.23637v2 Announce Type: replace Abstract: Quantum networks with independent sources allow observing quantum nonlocality or steering with just a single measurement per node of the network, or without any inputs. Inspired by the recently introduced notion of swap-steering, we consider here the triangle network scenario without inputs, where one of the parties is trusted to perform a well-calibrated measurement. In this scenario, we first propose a linear witness to detect triangle network swap-steering. Then, by using the correlations that achieve the maximum value of this inequality, and assuming that all the sources are the same, we can self-test the state generated by the sources and the measurements of the untrusted party. We then extend this framework to ring networks with an arbitrary number of nodes with one of them being trusted. Interestingly, this is the first example of a topologically robust, that is, one can observe steerability without assuming the network structure of the network, as well as noise-robust quantum advantage in a network. Additionally, by allowing the trusted party to perform tomography of their subsystems, we demonstrate that every bipartite entangled state will result in swap-steerable correlations in the ring network. For this purpose, we construct linear witnesses to detect ring network swap-steering corresponding to every bipartite entangled state.
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https://arxiv.org/abs/2506.23637
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229740d97677949aeff251a5c71a42a281b8f0fe816f274704ac4e98ace3fdc9
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2026-01-21T00:00:00-05:00
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Small Quantum Low Density Parity Check Codes for Near-Term Experiments
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arXiv:2507.09690v3 Announce Type: replace Abstract: It is widely accepted that quantum error correction is essential for realizing large-scale fault-tolerant quantum computing. Recent experiments have demonstrated error correction codes operating below threshold, primarily using local planar codes such as the surface code and color code. In parallel, theoretical advances in quantum low-density parity-check (LDPC) codes promise significantly lower overheads, albeit at the cost of requiring non-local parity checks. While these results are encouraging, implementing such codes remains challenging for near-term experiments, creating obstacles to holistic benchmarking of hardware architectures capable of supporting long-range couplers. In this work, we present a simple construction recipe for small quantum LDPC codes based on recent developments in the field. Our codes are approximately twice as efficient as comparable surface codes, yet require only weight-four parity checks, which simplifies experimental realization compared to other quantum LDPC codes. We provide concrete proposals for implementations with superconducting qubits in flip-chip architectures and with semiconductor spin qubits using shuttling-based approaches.
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https://arxiv.org/abs/2507.09690
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e910abfa101ffb2c6cbdbbe96394ed30db01c134474f0d4a68dd8b270febbe26
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2026-01-21T00:00:00-05:00
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A Simple Method of Evaluating Laser Diode Suitability for Phase-Noise Based QRNG
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arXiv:2507.17471v2 Announce Type: replace Abstract: Quantum random number generators (QRNGs) based on semiconductor laser phase noise are an inexpensive and efficient resource for true random numbers. Commercially available technology allows for designing QRNG setups tailored to specific use cases. However, it is important to constantly monitor whether the QRNG is performing according to the desired security standards in terms of independence and uniform distribution of the generated numbers. This is especially important in cryptographic applications. This paper presents a test scheme that helps to assess the acceptable operating conditions of a semiconductor laser for QRNG operation, using commonly accessible methods. This can be used for system monitoring, but crucially also to help the user choose the laser diode which better suits their needs. Two specific quality measurements, ensuring proper operation of the device, are explained and discussed. Setup-specific approaches for setting an acceptance boundary for these measures are presented and exemplary measurement data showing their effectiveness is given. By following the comprehensible procedure described here, a QRNG qualification environment tailored to specific security requirements can be reproduced.
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https://arxiv.org/abs/2507.17471
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3015077268c2c2f7e76817217c8346c82cb536d35db49ba4b2975c71afc04ab1
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2026-01-21T00:00:00-05:00
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Quantum Advantage in Identifying the Parity of Permutations with Certainty
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arXiv:2508.04310v2 Announce Type: replace Abstract: We establish a sharp quantum advantage in determining the parity (even/odd) of an unknown permutation applied to any number $n \ge 3$ of particles. Classically, this is impossible with fewer than $n$ labels, being that the success is limited to random guessing. Quantum mechanics does it with certainty with as few as $\lceil \sqrt{n}\, \rceil$ distinguishable states per particle, thanks to entanglement. Below this threshold, not even quantum mechanics helps: both classical and quantum success are limited to random guessing. For small $n$, we provide explicit expressions for states that ensure perfect parity identification. We also assess the minimum entanglement these states need to carry, finding it to be close to maximal, and even maximal in some cases. The task requires no oracles or contrived setups and provides a simple, rigorous example of genuine quantum advantage.
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https://arxiv.org/abs/2508.04310
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40f3480470e9d171994e1a902249c5c01aa87a09384e31e356063eecec5f23ee
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2026-01-21T00:00:00-05:00
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Tuning of SiV quantum emission in nitrogen-doped nanodiamonds by dual-color excitation
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arXiv:2509.06500v2 Announce Type: replace Abstract: The charge dynamics of silicon-vacancy (SiV) centers have been investigated for the first time in high-pressure high-temperature nanodiamonds (NDs) with varying concentrations of substitutional nitrogen (Ns). We demonstrate a controlled sixfold enhancement of SiV- photoluminescence (PL) under dual-color excitation, consisting of strong red (~660 nm) illumination combined with weak green (~530 nm) excitation. The measured dependencies of SiV- PL lifetime and intensity on excitation wavelength, together with the enhancement dependence on Ns concentration in the studied nanodiamonds, provide unambiguous evidence of the involvement of donor nitrogen in SiV-emission dynamics. Saturation curves and second-order PL intensity correlation measurements further indicate suppression of the population of the optically inactive SiV2- state upon the addition of green excitation. These results unlock a practical pathway toward engineering optically-controlled and scalable quantum emitters based on SiV-luminescent diamond nanoparticles.
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https://arxiv.org/abs/2509.06500
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1b4c867c1870b7f737e13ababa0639016d754568f013342a9e5226418eb2096f
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2026-01-21T00:00:00-05:00
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Universal quantum control over bosonic network
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arXiv:2509.06560v2 Announce Type: replace Abstract: Perfect transfer of {\em unknown} states across distinct nodes is a basic function in bosonic quantum networks. Here we develop a general theory to construct an $N$-node bosonic network governed by the time-dependent Hamiltonian, as the universal quantum control theory for continuous-variable systems. In particular, we can activate nonadiabatic passages superposed of initial and target modes by the commutation condition about the Hamiltonian's coefficient matrix and projection operator in the representation of time-independent ancillary modes, which serves as the necessary and sufficient condition to solve the time-dependent Schr\"odinger equation of the full Hamiltonian. To exemplify the versatility of our theory on the Heisenberg-picture passages, we perform arbitrary state exchange between two nodes, chiral entanglement transfer among three bosonic nodes, and chiral Fock-state transfer among three of four bosonic nodes. Our work provides a promising avenue toward the universal control of any pair of nodes or modes as well as the entire bosonic network.
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https://arxiv.org/abs/2509.06560
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fd8ca4ae1f2d391a10b73947e288c712f08a64a4cb3de46449a752c2892f71a6
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2026-01-21T00:00:00-05:00
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Cost-aware Photonic Graph State Generation: A Graphical Framework
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arXiv:2509.22777v2 Announce Type: replace Abstract: Photonic graph states are essential resources for quantum computation and communication. Deterministic emitter-based generation of graph states overcomes the scalability issues of probabilistic approaches; nonetheless, their experimental realization is constrained by technological demands, often expressed by the number of two-qubit gates and the depth and/or width of the quantum circuits used to model the generation process. Here, we introduce a cost-aware framework for the generation of photonic graph states of arbitrary size and shape, built on a complete set of necessary and sufficient conditions and a universal set of elementary graph operations that govern the evolution of the state toward the target. Within this framework, we develop Graph Builder, a deterministic generation algorithm that achieves substantial reductions (up to an order of magnitude) in two-qubit gate usage for both random and structured graphs, compared with alternative approaches. Furthermore, we show that this framework enables the identification of elementary building blocks in specific cases, such as encoded 6-ring states. The algorithm uses the minimum number of emitters possible for a fixed emission sequence, while also supporting the use of extra emitters for controlled trade-offs between emitter count and other cost metrics. Moreover, by systematically identifying the degrees of freedom at each stage of the generation process, this framework fully characterizes the optimization landscape, enabling analytic, heuristic, or exhaustive strategies for further cost reductions. Our approach provides a general and versatile tool for designing and optimizing emitter-based photonic graph state generation protocols, essential for scalable and resource-efficient photonic quantum information processing.
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https://arxiv.org/abs/2509.22777
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4c7b03ba3837efdfd68e1bcb02c6f0921c2d8cfdd0847f1846478993f5943108
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2026-01-21T00:00:00-05:00
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Approximate Quantum State Preparation with Tree-Based Bayesian Optimization Surrogates
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arXiv:2510.00145v3 Announce Type: replace Abstract: We study the problem of approximate state preparation on near-term quantum computers, where the goal is to construct a parameterized circuit that reproduces the output distribution of a target quantum state while minimizing resource overhead. This task is especially relevant for near-term algorithms where distributional matching suffices, but it is challenging due to stochastic outputs, limited circuit depth, and a high-dimensional, non-smooth parameter space. We propose CircuitTree, a surrogate-guided optimization framework based on Bayesian Optimization with tree-based models, which avoids the scalability and smoothness assumptions of Gaussian Process surrogates. Our framework introduces a structured layerwise decomposition strategy that partitions parameters into blocks aligned with variational circuit architecture, enabling distributed and sample-efficient optimization with theoretical convergence guarantees. Empirical evaluations on synthetic benchmarks and variational tasks validate our theoretical insights, showing that CircuitTree achieves low total variation distance and high fidelity while requiring significantly shallower circuits than existing approaches.
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https://arxiv.org/abs/2510.00145
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9567f07fb40d4e45832f9125965961c99acdb194b5aabcf22e19bfa8910fb460
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2026-01-21T00:00:00-05:00
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Angular--Momentum--Resolved Aharonov--Bohm Coupling Energy
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arXiv:2510.06016v2 Announce Type: replace Abstract: We present an angular--momentum--resolved energetic formulation of the Aharonov--Bohm (AB) response for a confined Dirac electron based on two gauge--invariant interaction functionals: a magnetization--field functional and a current--potential functional. Using exact Dirac eigenmodes in a cylindrical cavity threaded by a solenoidal flux, we show that the magnetization--field functional yields a core--localized interaction energy restricted to the $l=0$ channel, with all higher angular--momentum contributions suppressed and vanishing entirely in the limit $a\!\to\!0$. The current--potential functional, by contrast, produces a finite, mode--dependent energy shift for $l\!\ge\!1$ in the same limit, arising from a local interaction between the solenoidal vector potential and the spatially distributed Dirac current, and explicitly encoding the geometric and topological structure of the coupling energy.
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https://arxiv.org/abs/2510.06016
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17413a58dfc23982a0c583e468998f45d019e329f1f63ddd7159c684db0e8306
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2026-01-21T00:00:00-05:00
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Exact WKB method for radial Schr\"odinger equation
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arXiv:2510.11766v3 Announce Type: replace Abstract: We revisit exact WKB quantization for radial Schr\"odinger problems from the modern resurgence perspective, with emphasis on how ``physically meaningful'' quantization paths should be chosen and interpreted. Using connection formulae at simple turning points and at regular singular points, we show that the nontrivial-cycle data give the spectrum. In particular, for the $3$-dimensional harmonic oscillator and the $3$-dimensional Coulomb potential, we explicitly compute a closed contour which starts at $+\infty$, bulges into the $r<0$ sector to encircle the origin, and returns to $+\infty$. Also we propose that the appropriate slice of the closed path provides a physical local basis at $r=0$, which is used by an origin-to-$\infty$ open path. Via the change of variables $r=e^x$ ($x\in(-\infty,\infty)$), the origin data are pushed to the boundary condition of convergence at $x\to-\infty$, which renders the equivalence between open-connection and closed-cycle quantization transparent. The Maslov contribution from the regular singularity is incorporated either as a small-circle monodromy which is justified in terms of renormalization group, or, equivalently, as a boundary phase; we also develop an optimized/variational perturbation theory on exact WKB. Our analysis clarifies, in radial settings, how mathematical monodromy data and physical boundary conditions dovetail, thereby addressing recent debates on path choices in resurgence-based quantization.
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https://arxiv.org/abs/2510.11766
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f97c0b3ab32e5c5baf5881273a95741293de06be8716f4129887e9ce49b70502
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2026-01-21T00:00:00-05:00
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Quantum State Designs via Magic Teleportation
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arXiv:2510.13950v2 Announce Type: replace Abstract: We investigate how non-stabilizer resources enable the emergence of quantum state designs within the projected ensemble. Starting from initial states with finite magic and applying resource-free Clifford circuits to scramble them, we analyze the ensemble generated by performing projective Pauli measurements on a subsystem of the final state. Using both analytical arguments and large-scale numerics, we show that the projected ensemble converges towards a state $k$-design with an error that decays exponentially with the $k$-th Stabilizer R\'enyi Entropy of the pre-measurement state, via a Magic-Induced Design Ansatz (MIDA) that we introduce. We identify a universal scaling form, valid across different classes of magic initial states, and corroborate it through numerical simulations and analytical calculations of the frame potential. For finite-depth Clifford unitaries, we show that the timescales at which state designs emerge are controlled by the transport of magic. We identify a ``magic teleportation'' mechanism whereby non-Clifford resources injected locally spread through Clifford scrambling and measurements across distances beyond the lightcone. Our results demonstrate how a small and controlled amount of magic suffices to generate highly random states, providing a systematic route toward generating quantum state designs in early fault-tolerant devices.
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https://arxiv.org/abs/2510.13950
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3075c478572aac94840a8fa4010925bb2e55b86f13e13682e461065c002e2fdc
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2026-01-21T00:00:00-05:00
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Macroscopic quantum phenomena and quantum computing
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arXiv:2510.19846v2 Announce Type: replace Abstract: This News & Views article provides a perspective on the 2025 Nobel Prize in Physics, including the groundbreaking discovery of macroscopic quantum tunneling and energy quantization in superconducting circuits, the history and causes giving rise to this breakthrough, and its impact on subsequent progress in quantum computing.
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https://arxiv.org/abs/2510.19846
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Academic Papers
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9e5cb51b098d2262d2f7ff539719921a6e6e5f303f75cce480789edd73c1a112
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2026-01-21T00:00:00-05:00
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Measurement-only circuit of perturbed toric code on triangular lattice: Topological entanglement, 1-form symmetry and logical qubits
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arXiv:2510.23162v3 Announce Type: replace Abstract: Measurement-only (quantum) circuit (MoC) gives possibility to realize the states with rich entanglements, topological orders and quantum memories. This work studies the MoC, in which the projective-measurement operators consist of stabilizers of the toric code and competitive local Pauli operators. The former correspond to terms of the toric code on a triangular lattice and the later to external magnetic and electric fields. We employ efficient numerical stabilizer algorithm to trace evolving states undergoing phase transitions. We elucidate the phase diagram of the MoC system with the observables such as, topological entanglement entropy (TEE), disorder parameters of 1-form symmetries and emergent logical operators. We clarify the locations of the phase transitions through the observation of the above quantities and obtain precise critical exponents to examine if the observables exhibit the critical behavior simultaneously under the MoC and transitions belong to the same universality class. In contrast to the TC Hamiltonian system and toric code MoC on a square lattice, the system on the triangular lattice is not self-dual nor bipartite, and then, coincidence by symmetries, such as critical behaviors across the TC and Higgs/confined phase, does not takes place. Then, the toric code MoC on the triangular lattice provides us a suitable playground to clarify the mutual relationship between the TEE, spontaneous symmetry breaking of the 1-form symmetries, and emergence of logical operators. Obtained results indicate that toric code MoC on the triangular lattice exhibits a few distinct phase transitions with different location and critical exponents, and some of them are closely related with the two-dimensional percolation transition.
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https://arxiv.org/abs/2510.23162
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91c8e376d4cb2263c3d8cda782de312f016b6c5ace3d7750a06a53eccfd30eef
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2026-01-21T00:00:00-05:00
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Overcoming disorder in superconducting globally driven quantum computing
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arXiv:2510.25996v2 Announce Type: replace Abstract: We study the impact of static disorder on a globally-controlled superconducting quantum computing architecture based on a quasi-two-dimensional ladder geometry [R. Menta et al., Phys. Rev. Research 7, L012065 (2025)]. Specifically, we examine how fabrication-induced inhomogeneities in qubit resonant frequencies and coupling strengths affect quantum state propagation and the fidelity of fundamental quantum operations. Using numerical simulations, we quantify the degradation in performance due to disorder and identify single-qubit rotations, two-qubit entangling gates, and quantum information transport as particularly susceptible. To address this challenge, we rely on pulse optimization schemes, and, in particular, on the GRAPE (Gradient Ascent Pulse Engineering) algorithm. Our results demonstrate that, even for realistic levels of disorder, optimized pulse sequences can achieve high-fidelity operations, exceeding 99.9% for the three quantum operations, restoring reliable universal quantum logic and robust information flow. These findings highlight pulse optimization as a powerful strategy to enhance the resilience to disorder of solid-state globally-driven quantum computing platforms.
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https://arxiv.org/abs/2510.25996
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102ea5e59e52b2bd7600478fe98e14395bda1edabf9bb35de9112a1538554a44
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2026-01-21T00:00:00-05:00
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Optimizing quantum violation for multipartite facet Bell inequalities
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arXiv:2511.07523v2 Announce Type: replace Abstract: Nonlocality shapes quantum correlations, revealed through the violation of Bell inequalities. The intersection of all valid Bell inequalities is the so-called local polytope. In multipartite systems, characterizing the local polytope quickly becomes an intractable task as the system size increases. Optimizing Bell inequalities to maximize the ratio between their quantum value and classical bound is key to understanding multipartite nonlocality. We propose a gradient-based method for this optimization. Numerical results indicate that local maxima of this ratio typically correspond to facet Bell inequalities of the local polytope. This enables an iterative search for tight and robust Bell inequalities. Applied to permutation-invariant scenarios, the method provides tight Bell inequalities with large quantum violations and facilitates experimental certification of Bell correlations without full knowledge of the local polytope. Moreover, analytical results of the maximum ratio are derived in the thermodynamic limit.
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https://arxiv.org/abs/2511.07523
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40745a3d4b43ddd08eb70cdeed7fa1b8d006707f6385c83c53ee91d134947e64
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2026-01-21T00:00:00-05:00
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Separating QMA from QCMA with a classical oracle
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arXiv:2511.09551v2 Announce Type: replace Abstract: We construct a classical oracle proving that, in a relativized setting, the set of languages decidable by an efficient quantum verifier with a quantum witness (QMA) is strictly bigger than those decidable with access only to a classical witness (QCMA). The separating classical oracle we construct is for a decision problem we coin spectral Forrelation -- the oracle describes two subsets of the boolean hypercube, and the computational task is to decide if there exists a quantum state whose standard basis measurement distribution is well supported on one subset while its Fourier basis measurement distribution is well supported on the other subset. This is equivalent to estimating the spectral norm of a "Forrelation" matrix between two sets that are accessible through membership queries. Our lower bound derives from a simple observation that a query algorithm with a classical witness can be run multiple times to generate many samples from a distribution, while a quantum witness is a "use once" object. This observation allows us to reduce proving a QCMA lower bound to proving a sampling hardness result which does not simultaneously prove a QMA lower bound. To prove said sampling hardness result for QCMA, we observe that quantum access to the oracle can be compressed by expressing the problem in terms of bosons -- a novel "second quantization" perspective on compressed oracle techniques, which may be of independent interest. Using this compressed perspective on the sampling problem, we prove the sampling hardness result, completing the proof.
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https://arxiv.org/abs/2511.09551
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41f4c89577e1cbf3738e7b2a56d0e7feea79ceeb718e7a0d4f69e847f1390637
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2026-01-21T00:00:00-05:00
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TRAM: A Transverse Relaxation Time-Aware Qubit Mapping Algorithm for NISQ Devices
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arXiv:2511.16051v2 Announce Type: replace Abstract: Noisy intermediate-scale quantum (NISQ) devices impose dual challenges on quantum circuit execution: limited qubit connectivity requires extensive SWAP-gate routing, while time-dependent decoherence progressively degrades quantum information. Existing qubit mapping algorithms optimize for hardware topology and static calibration metrics but systematically neglect transverse relaxation dynamics (T2), creating a fundamental gap between compiler decisions and evolving noise characteristics. We present TRAM (Transverse Relaxation Time-Aware Qubit Mapping), a coherence-guided compilation framework that elevates decoherence mitigation to a primary optimization objective. TRAM integrates calibration-informed community detection to construct noise-resilient qubit partitions, generates time-weighted initial mappings that anticipate coherence decay, and dynamically schedules SWAP operations to minimize cumulative error accumulation. Evaluated on Qiskit-based simulators with realistic noise models, TRAM outperforms SABRE by 3.59% in fidelity, reduces gate count by 11.49%, and shortens circuit depth by 12.28%, establishing coherence-aware optimization as essential for practical quantum compilation in the NISQ era.
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https://arxiv.org/abs/2511.16051
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1a9a1d37c6254042d9ea63d38741f83069e0b018de6d1303ffff20c287da9c0f
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2026-01-21T00:00:00-05:00
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COMPAS: A Distributed Multi-Party SWAP Test for Parallel Quantum Algorithms
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arXiv:2511.23434v2 Announce Type: replace Abstract: The limited number of qubits per chip remains a critical bottleneck in quantum computing, motivating the use of distributed architectures that interconnect multiple quantum processing units (QPUs). However, executing quantum algorithms across distributed systems requires careful co-design of algorithmic primitives and hardware architectures to manage circuit depth and entanglement overhead. We identify multivariate trace estimation as a key subroutine that is naturally suited for distribution, and broadly useful in tasks such as estimating R\'enyi entropies, virtual cooling and distillation, and certain applications of quantum signal processing. In this work, we introduce COMPAS, an architecture that realizes multivariate trace estimation across a multi-party network of interconnected modular and distributed QPUs by leveraging pre-shared entangled Bell pairs as resources. COMPAS adds only a constant depth overhead and consumes Bell pairs at a rate linear in circuit width, making it suitable for near-term hardware. Unlike other schemes, which must choose between asymptotic optimality in circuit depth or GHZ width, COMPAS achieves both at once. Additionally, we analyze network-level errors and simulate the effects of circuit-level noise on the architecture.
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https://arxiv.org/abs/2511.23434
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79bef6606d8158998665c531d079465aa2d2836cdb70a19c31eae38e32998e1a
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2026-01-21T00:00:00-05:00
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Information-efficient decoding of surface codes
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arXiv:2512.14255v2 Announce Type: replace Abstract: Surface codes are a popular error-correction route to fault-tolerant quantum computation. The so-called exponential backlog problem that can arise when one has to do logical $T$-gates within the surface code demands real-time decoding of the syndrome information to diagnose the appropriate Pauli frame in which to do the gate. This in turn puts a minimum requirement on the communication rate between the quantum processing unit, where the syndrome information is collected, and the classical processor, where the decoding algorithm is run. This minimum communication rate can be difficult to achieve while preserving the quality of the quantum processor. Here, we present two decoders that make use of a reduced syndrome information volume, relying on a number of syndrome bits that scale only as the width -- and not the usual area -- of the surface-code patch. This eases the communication requirements necessary for real-time decoding.
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https://arxiv.org/abs/2512.14255
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aa345e7028aadd2eaa2b08a0ed7794f435228d7313949190be9af15fe155b2f6
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2026-01-21T00:00:00-05:00
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Improved Lower Bounds for QAC0
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arXiv:2512.14643v2 Announce Type: replace Abstract: In this work, we prove the strongest known lower bounds for QAC$^0$, allowing polynomially many gates and ancillae. Our main results show that: (1) Depth-3 QAC$^0$ circuits cannot compute PARITY, and require $\Omega(\exp(\sqrt{n}))$ gates to compute MAJORITY. (2) Depth-2 circuits cannot approximate high-influence Boolean functions (e.g., PARITY) with non-negligible advantage, regardless of size. We develop new classical simulation techniques for QAC$^0$ to obtain our depth-3 bounds. In these results, we relax the output requirement of the quantum circuit to a single bit, making our depth $2$ approximation bound stronger than the previous best bound of Rosenthal (2021). This also enables us to draw natural comparisons with classical AC$^0$ circuits, which can compute PARITY exactly in depth $2$ (exp size). Our techniques further suggest that, for boolean total functions, constant-depth quantum circuits do not necessarily provide more power than their classical counterparts. Our third result shows that depth $2$ QAC$^0$ circuits, regardless of size, cannot exactly synthesize an $n$-target nekomata state (a state whose synthesis is directly related to the computation of PARITY). This complements the depth $2$ exponential size upper bound of Rosenthal (2021) for approximating nekomatas (which is used as a sub-circuit in the only known constant depth PARITY upper bound). Finally, we argue that approximating PARITY in QAC0, with significantly better than 1/poly(n) advantage on average, is just as hard as computing it exactly. Thus, extending our techniques to higher depths would also rule out approximate circuits for PARITY and related problems
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https://arxiv.org/abs/2512.14643
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54595ad484687fae9b286e289325d836a4bf70b226bfb984099afe2b891281bc
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2026-01-21T00:00:00-05:00
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Real Matrix Representations of Quantum Operators: An Introduction to Quantum Index Algebra
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arXiv:2512.19977v2 Announce Type: replace Abstract: We introduce Quantum Index Algebra (QIA) as a finite, index-based algebraic framework for representing and manipulating quantum operators on Hilbert spaces of dimension $2^m$. In QIA, operators are expressed as structured combinations of basis elements indexed by Boolean codes, allowing products, commutators, and conjugations to be computed through finite rules on discrete indices rather than through dense matrix arithmetic. This representation unifies combinatorial index structure, explicit matrix realization, and transformation properties under Walsh-Hadamard-type transforms within a single formalism. Using QIA and its associated block-matrix realization, we reformulate the Bernstein-Vazirani hidden-string problem in its phase-oracle form entirely within a real, finite-dimensional algebraic setting. We show that, under structured oracle access, the QIA procedure reproduces the Bernstein-Vazirani algorithm exactly and achieves the same asymptotic query complexity and circuit depth as the standard quantum algorithm. In particular, the hidden string is recovered by symbolic manipulation of a sparse algebraic representation of the oracle rather than by numerical simulation of quantum amplitudes. Our results demonstrate that the apparent quantum speed-up in this setting is a consequence of operator structure rather than Hilbert-space dimensionality alone. QIA thus provides a precise language for separating genuinely quantum resources from those arising from algebraic and combinatorial structures and offers a new perspective on the classical simulability of structured quantum circuits.
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https://arxiv.org/abs/2512.19977
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845ab8fd47cbf215b224199f773a4684b3ffa4748c533d7d617098246c8704ee
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2026-01-21T00:00:00-05:00
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Efficient Calculation of the Maximal R\'{e}nyi Divergence for a Matrix Product State via Generalized Eigenvalue Density Matrix Renormalization Group
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arXiv:2601.02122v2 Announce Type: replace Abstract: The study of quantum and classical correlations between subsystems is fundamental to understanding many-body physics. In quantum information theory, the quantum mutual information, $I(A;B)$, is a measure of correlation between the subsystems $A,B$ in a quantum state, and is defined by the means of the von Neumann entropy: $I\left(A;B\right)=S\left(\rho_{A}\right)+S\left(\rho_{B}\right)-S\left(\rho_{AB}\right)$. However, such a computation requires an exponential amount of resources. This is a defining feature of quantum systems, the infamous ``curse of dimensionality'' . Other measures, which are based on R\'{e}nyi divergences instead of von Neumann entropy, were suggested as alternatives in a recent paper showing them to possess important theoretical features, and making them leading candidates as mutual information measures. In this work, we concentrate on the maximal R\'{e}nyi divergence. This measure can be shown to be the solution of a generalized eigenvalue problem. To calculate it efficiently for a 1D state represented as a matrix product state, we develop a generalized eigenvalue version of the density matrix renormalization group algorithm. We benchmark our method for the paradigmatic XXZ chain, and show that the maximal R\'enyi divergence may exhibit different trends than the von Neumann mutual information.
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https://arxiv.org/abs/2601.02122
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dae365b06d7f9d79923a0ba003166ea7a98e2cdae4ca77c9c034768407ea69d2
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2026-01-21T00:00:00-05:00
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Holographic codes seen through ZX-calculus
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arXiv:2601.04467v2 Announce Type: replace Abstract: We re-visit the pentagon holographic quantum error correcting code from a ZX-calculus perspective. By expressing the underlying tensors as ZX-diagrams, we study the stabiliser structure of the code via Pauli webs. In addition, we obtain a diagrammatic understanding of its logical operators, encoding isometries, R\'enyi entropy and toy models of black holes/wormholes. Then, motivated by the pentagon holographic code's ZX-diagram, we introduce a family of codes constructed from ZX-diagrams on its dual hyperbolic tessellations and study their logical error rates using belief propagation decoders.
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https://arxiv.org/abs/2601.04467
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62aecb1e8db03a03f95235f8e33b5e3b52d6e8e718a04ea6a7952c088c0786f4
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2026-01-21T00:00:00-05:00
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Maximal Entanglement and Frozen Information: A Unified Framework for Dynamical Quantum Phase Transitions
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arXiv:2601.04535v2 Announce Type: replace Abstract: Dynamical quantum phase transitions (DQPTs) are temporal singularities marked by zeros of the Loschmidt echo, yet their underlying quantum-information structure remains elusive. Here, we introduce a momentum-resolved entanglement entropy as a direct probe of DQPTs in translation-invariant free systems. We analytically establish that every critical momentum mode $k^{*}$ associated with a DQPT saturates its entanglement to the maximal value $\ln{2}$, coinciding with the vanishing of the Loschmidt echo. Crucially, we demonstrate that this maximal entanglement universally suppresses information scrambling: a momentum-resolved out-of-time-ordered correlator (OTOC) vanishes identically for all times at $k^{*}$. These three signatures -- Fisher zeros, maximal entanglement, and vanished OTOC -- are proved to be equivalent in both the transverse-field Ising and Su-Schrieffer-Heeger models, despite their distinct bipartitions (momentum-pair vs. sublattice). Our results establish a unified, information-theoretic framework for DQPTs, revealing them a points where quantum correlations saturate and information flow halts. This work elevates entanglement and scrambling to central dynamical order parameters, offering a universal perspective on nonequilibrium quantum critically.
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https://arxiv.org/abs/2601.04535
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5a9f8632eb7fce8381ce4c915331edd1137ba571a53bb3599872fb250859a063
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2026-01-21T00:00:00-05:00
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Breaking the Orthogonality Barrier in Quantum LDPC Codes
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arXiv:2601.08824v3 Announce Type: replace Abstract: Classical low-density parity-check (LDPC) codes are a widely deployed and well-established technology, forming the backbone of modern communication and storage systems. It is well known that, in this classical setting, increasing the girth of the Tanner graph while maintaining regular degree distributions leads simultaneously to good belief-propagation (BP) decoding performance and large minimum distance. In the quantum setting, however, this principle does not directly apply because quantum LDPC codes must satisfy additional orthogonality constraints between their parity-check matrices. When one enforces both orthogonality and regularity in a straightforward manner, the girth is typically reduced and the minimum distance becomes structurally upper bounded. In this work, we overcome this limitation by using permutation matrices with controlled commutativity and by restricting the orthogonality constraints to only the active part of the construction, while preserving regular check-matrix structures. This design circumvents conventional structural distance limitations induced by parent-matrix orthogonality, and enables the construction of quantum LDPC codes with large girth while avoiding latent low-weight logical operators. As a concrete demonstration, we construct a girth-8, (3,12)-regular $[[9216,4612, \leq 48]]$ quantum LDPC code and show that, under BP decoding combined with a low-complexity post-processing algorithm, it achieves a frame error rate as low as $10^{-8}$ on the depolarizing channel with error probability $4 \%$.
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https://arxiv.org/abs/2601.08824
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32e41b5d21debd411b67ac8dfffc1664afbd94e90828a7bc77f89ea674f60153
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2026-01-21T00:00:00-05:00
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Reversing quantum dynamics with near-optimal quantum and classical fidelity
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arXiv:quant-ph/0004088v2 Announce Type: replace Abstract: We consider the problem of reversing quantum dynamics, with the goal of preserving an initial state's quantum entanglement or classical correlation with a reference system. We exhibit an approximate reversal operation, adapted to the initial density operator and the ``noise'' dynamics to be reversed. We show that its error in preserving either quantum or classical information is no more than twice that of the optimal reversal operation. Applications to quantum algorithms and information transmission are discussed.
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https://arxiv.org/abs/quant-ph/0004088
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232ed7c94b52ce1f0205c19f44256e8859824d0f2e4445155ce959bf2830f259
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2026-01-21T00:00:00-05:00
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Valley Splitting Correlations Across a Silicon Quantum Well Containing Germanium
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arXiv:2504.12455v3 Announce Type: replace-cross Abstract: Quantum dots in SiGe/Si/SiGe heterostructures host coherent electron spin qubits, which are promising for future quantum computers. The silicon quantum well hosts near-degenerate electron valley states, creating a low-lying excited state that is known to reduce spin qubit readout and control fidelity. The valley energy splitting is dominated by the microscopic disorder in the SiGe alloy and at the Si/SiGe interfaces, and while Si devices are compatible with large-scale semiconductor manufacturing, achieving a uniformly large valley splitting energy across a many-qubit device spanning mesoscopic distances is an outstanding challenge. In this work we study valley splitting variations in a 1D quantum dot array, formed in a Si$_{0.972}$Ge$_{0.028}$ quantum well, manufactured by Intel. We observe correlations in valley splitting, at both sub-100nm (single gate) and >1$\mu$m (device) lengthscales, that are consistent with alloy disorder-dominated theory and simulation. Our results develop the mesoscopic understanding of Si/SiGe heterostructures necessary for scalable device design.
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https://arxiv.org/abs/2504.12455
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da7db9262e9a1133048b7d0d2c5cca260c5278de79eb7eb33ee564699960ac4b
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2026-01-21T00:00:00-05:00
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Compton Form Factor Extraction using Quantum Deep Neural Networks
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arXiv:2504.15458v3 Announce Type: replace-cross Abstract: We extract Compton form factors (CFFs) from deeply virtual Compton scattering measurements at the Thomas Jefferson National Accelerator Facility (JLab) using quantum-inspired deep neural networks (QDNNs). The analysis implements the twist-2 Belitsky-Kirchner-M\"uller formalism and employs a fitting strategy that emulates standard local fits. Using pseudodata, we benchmark QDNNs against classical deep neural networks (CDNNs) and find that QDNNs often deliver higher predictive accuracy and tighter uncertainties at comparable model complexity. Guided by these results, we introduce a quantitative selection metric that indicates when QDNNs or CDNNs are optimal for a given experimental fit. After obtaining local extractions from the JLab data, we perform a standard neural-network global CFF fit and compare with previous global analyses. The results support QDNNs as an efficient and complementary tool to CDNNs for CFF determination and for future multidimensional studies of parton distributions and hadronic structure.
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https://arxiv.org/abs/2504.15458
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963fdd4f42c3a69b89ddbdef061d09c31c91c7e6fbf638fcc0f750b640a79f1b
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2026-01-21T00:00:00-05:00
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Acoustic phonons, spin-phonon coupling and spin relaxation via the lattice reorientation mechanism in hexagonal germanium nanowires
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arXiv:2504.18198v3 Announce Type: replace-cross Abstract: Spin relaxation via electron-phonon interaction is an important decoherence mechanism for spin qubits. In this work, we study spin relaxation in hexagonal (2H) germanium, a novel direct-gap semiconductor showing great potential to combine highly coherent spin qubits with optical functionality. Focusing on electrostatically defined quantum dots in hexagonal germanium nanowires, we (i) identify geometries where spin qubit experiments are feasible, (ii) compute the nanowire phonon modes, and (iii) describe spin relaxation of hole spin qubits due to phonon-induced lattice reorientation, a direct spin-phonon coupling mechanism that is absent in cubic semiconductors typically used for spin qubits (GaAs, cubic Si, cubic Ge). We obtain the spin relaxation time as a function of nanowire cross section, quantum dot confinement length, and magnetic field. For realistic parameters, we find relaxation times above 10 ms, and reveal that the magnetic field direction maximizing the relaxation time depends on the qubit Larmor frequency. Our results facilitate the design of nanowire quantum dot experiments with long qubit relaxation times.
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https://arxiv.org/abs/2504.18198
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186e5f26815421e0e4bb62979541cfe6c7b091ecbfedf13e248b1523ca0da60f
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2026-01-21T00:00:00-05:00
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Emergent Thermalization Thresholds in Unitary Dynamics of Inhomogeneously Disordered Quantum Systems
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arXiv:2505.11253v2 Announce Type: replace-cross Abstract: Inspired by the avalanche scenario for many-body localization (MBL) instability, we reverse the conventional set-up and ask whether a large weakly-disordered chain can thermalize a smaller, strongly-disordered chain when the composite system evolves unitarily. Using transport as a dynamical probe, we identify three distinct thermalization regimes as a function of the disorder strength of the smaller chain: (i) complete thermalization with self-averaging at weak disorder, (ii) realization-dependent thermalization with strong sample-to-sample fluctuations at intermediate disorder, and (iii) absence of thermalization at strong disorder. We find that for a fixed length of the smaller chain, the non-self-averaging regime broadens with the size of the weakly-disordered chain, revealing a nuanced interplay between disorder and system size. These results highlight how inhomogeneous disorder can induce emergent thermalization thresholds in closed quantum systems, providing direct access to disorder regimes where thermalization or its absence can be reliably observed.
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https://arxiv.org/abs/2505.11253
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50b8d56925f24cecac4cc76e2a625f1512444c2754c8442bdd5727f1448381ae
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2026-01-21T00:00:00-05:00
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Lattice models with subsystem/weak non-invertible symmetry-protected topological order
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arXiv:2505.11419v2 Announce Type: replace-cross Abstract: We construct a family of lattice models which possess subsystem non-invertible symmetry-protected topological (SPT) order and analyze their interface modes protected by the symmetry, whose codimension turns out to be more than one. We also propose 2+1d lattice models which belong to two different weak SPT phases distinguished by a combination of translational symmetry and non-invertible symmetry. We show that the interface between them exhibits an exotic Lieb-Schultz-Mattis (LSM) anomaly associated with a modulated symmetry, which cannot be factorized into a direct product of internal and translational symmetries.
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https://arxiv.org/abs/2505.11419
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031309940df71ee15570b2d2ea9dabd762accb7b83f51ffea01ac3a6cf8c25c0
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2026-01-21T00:00:00-05:00
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Finite-temperature entanglement and coherence in asymmetric bosonic Josephson junctions
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arXiv:2506.06224v2 Announce Type: replace-cross Abstract: We investigate the finite-temperature properties of a bosonic Josephson junction composed of N interacting atoms confined by a quasi-one-dimensional asymmetric double-well potential, modeled by the two-site Bose-Hubbard Hamiltonian. We compute numerically the spectral decomposition of the statistical ensemble of states, the thermodynamic and entanglement entropies, the population imbalance, the quantum Fisher information, and the coherence visibility. We analyze their dependence on the system parameters, showing in particular how finite temperature and on-site energy asymmetry affect the entanglement and coherence properties of the system. Moreover, starting from a quantum phase model which accurately describes the system over a wide range of interactions, we develop a reliable description of the strong tunneling regime, where thermal averages may be computed analytically using a modified Boltzmann weight involving an effective temperature. We discuss the possibility of applying this effective description to other models in suitable regimes.
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https://arxiv.org/abs/2506.06224
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a757c53e3c542679dcd95c4f9497685e9e4b83ca4e8f48faba403af82f1df00d
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2026-01-21T00:00:00-05:00
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Emergence of cosmic structure from Planckian discreteness
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arXiv:2506.15413v2 Announce Type: replace-cross Abstract: In the standard inflationary paradigm the inhomogeneities observed in the CMB arise from quantum fluctuations of an initially homogeneous and isotropic vacuum state. This picture suffers from two well-known weaknesses. First, it assumes that quantum field theory remains valid at trans-Planckian scales, without modifications from quantum gravity. Second, it necessitates a quantum-to-classical transition in which fluctuations of a homogeneous quantum state become the classical inhomogeneities seen in the CMB. Recently, an alternative paradigm has been proposed in which such inhomogeneities are present from the very beginning, emerging from the assumed discreteness of spacetime at the Planck scale predicted by certain approaches to quantum gravity. Within this framework, scale-invariant scalar perturbations are generated naturally, without relying on trans-Planckian assumptions or invoking a quantum-to-classical transition. Specifically, inhomogeneities in the quantum state at the Planck scale propagate into semiclassical inhomogeneities on CMB scales. Here, we extend the aforementioned proposal to the most realistic case of a quasi-de Sitter expansion; in particular, we compute the scalar perturbation spectrum as a function of the slow-roll parameters, systematically encoded through the Hubble flow functions.
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https://arxiv.org/abs/2506.15413
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b51172cea7e220e409ba56b7d560461983751e96fe54dcc6de6ad5079ef16c0c
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2026-01-21T00:00:00-05:00
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Surrogate Modeling via Factorization Machine and Ising Model with Enhanced Higher-Order Interaction Learning
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arXiv:2507.01389v2 Announce Type: replace-cross Abstract: Recently, a surrogate model was proposed that employs a factorization machine to approximate the underlying input-output mapping of the original system, with quantum annealing used to optimize the resulting surrogate function. Inspired by this approach, we propose an enhanced surrogate model that incorporates additional slack variables into both the factorization machine and its associated Ising representation thereby unifying what was by design a two-step process into a single, integrated step. During the training phase, the slack variables are iteratively updated, enabling the model to account for higher-order feature interactions. We apply the proposed method to the task of predicting drug combination effects. Experimental results indicate that the introduction of slack variables leads to a notable improvement of performance. Our algorithm offers a promising approach for building efficient surrogate models that exploit potential quantum advantages.
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https://arxiv.org/abs/2507.01389
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dac84d49e951a7bb16dd8df2fde4751521abbf234e83f65812df4f7f5dcf9686
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2026-01-21T00:00:00-05:00
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Quantum Bootstrap Approach to a Non-Relativistic Potential for Quarkonium systems
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arXiv:2508.02916v2 Announce Type: replace-cross Abstract: The quantum bootstrap method is applied to determine the bound-state spectrum of Quarkonium systems using a non-relativistic potential approximation. The method translates the Schr\"odinger equation into a set of algebraic recursion relations for radial moments $\langle r^m \rangle$, which are constrained by the positive semidefiniteness of their corresponding Hankel matrices. The numerical implementation is first validated by calculating the $1S$ and $1P$ mass centroids for both charmonium ($c\bar{c}$) and bottomonium ($b\bar{b}$) systems, finding deviations of less than 0.5\% from experimental data from the Particle Data Group (PDG). This analysis is then extended to the hypothetical toponium ($t\bar{t}$) system, predicting a $1S$ ground state mass of $M \approx 344.3 \text{ GeV}$. This theoretical mass is in agreement with the energy of the recently observed resonance-like enhancement in the $t\bar{t}$ cross-section by the ATLAS and CMS collaborations. This result provides theoretical support for the interpretation of this experimental phenomenon as the formation of a quasi-bound toponium state and highlights the predictive power of the non-relativistic potential approach for systems of two massive quarks.
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https://arxiv.org/abs/2508.02916
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Academic Papers
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9d6dacc90ee09bd11cb46d49bc37f94fa000934b4fc460a87a7e8970b2b42ce4
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2026-01-21T00:00:00-05:00
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There and Back Again: A Gauging Nexus between Topological and Fracton Phases
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arXiv:2509.19440v2 Announce Type: replace-cross Abstract: Coupled layer constructions are a valuable tool for capturing the universal properties of certain interacting quantum phases of matter in terms of the simpler data that characterizes the underlying layers. In the study of fracton phases, the X-Cube model in 3+1D can be realized via such a construction by starting with a stack of 2+1D Toric Codes and turning on a coupling which condenses a composite "particle-string" object. In a recent work [Phys. Rev. B 112, 125124 (2025)], we have demonstrated that in fact, the particle-string can be viewed as a symmetry defect of a topological 1-form symmetry. In this paper, we study the result of gauging this symmetry in depth. We unveil a rich gauging web relating the X-Cube model to symmetry protected topological (SPT) phases protected by a mix of subsystem and higher-form symmetries, subsystem symmetry fractionalization in the 3+1D Toric Code, and non-trivial extensions of topological symmetries by subsystem symmetries. Our work emphasizes the importance of topological symmetries in non-topological, geometric phases of matter.
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https://arxiv.org/abs/2509.19440
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Academic Papers
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svg
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1cf1ea67d34f99b9074a40a8a1097d0d8eed912f3ef43849c4f109e9dabde10f
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2026-01-21T00:00:00-05:00
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Slow dynamics from a nested hierarchy of frozen states
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arXiv:2510.03159v3 Announce Type: replace-cross Abstract: We identify the mechanism of slow heterogeneous relaxation in quantum kinetically constrained models (KCMs) in which the potential energy strength is controlled by a coupling parameter. The regime of slow relaxation includes the large-coupling limit. By expanding around that limit, we reveal a \emph{nested hierarchy} of states that remain frozen on time scales determined by powers of the coupling. The classification of such states, together with the evolution of their Krylov complexity, reveals that these time scales are related to the distance between the sites where facilitated dynamics is allowed by the kinetic constraint. While correlations within frozen states relax slowly and exhibit metastable plateaus that persist on time scales set by powers of the coupling parameter, the correlations in the rest of the states decay rapidly. We compute the plateau heights of correlations across all frozen states up to second-order corrections in the inverse coupling. Our results explain slow relaxation in quantum KCMs and elucidate dynamical heterogeneity by relating the relaxation times to the spatial separations between the active regions.
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https://arxiv.org/abs/2510.03159
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Academic Papers
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svg
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b8d3efc630540720630ae5d8fc60e7c5e3810d54f3420215c1e7716a48a44ed6
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2026-01-21T00:00:00-05:00
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When Abstraction Breaks Physics: Rethinking Modular Design in Quantum Software
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arXiv:2510.18557v2 Announce Type: replace-cross Abstract: Abstraction is a fundamental principle in classical software engineering, which enables modularity, reusability, and scalability. However, quantum programs adhere to fundamentally different semantics, such as unitarity, entanglement, the no-cloning theorem, and the destructive nature of measurement, which introduce challenges to the safe use of classical abstraction mechanisms. This paper identifies a fundamental conflict in quantum software engineering: abstraction practices that are syntactically valid may violate the physical constraints of quantum computation. We present three classes of failure cases where naive abstraction breaks quantum semantics and propose a set of design principles for physically sound abstraction mechanisms. We further propose research directions, including quantum-specific type systems, effect annotations, and contract-based module design. Our goal is to initiate a systematic rethinking of abstraction in quantum software engineering, based on quantum semantics and considering engineering scalability.
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https://arxiv.org/abs/2510.18557
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Academic Papers
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svg
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0c56e9f07adcf4ee7f90f9e96b6561a1b4a9969ec1d014fbe85b83ab9fc0bafb
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2026-01-21T00:00:00-05:00
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Cosmological Entanglement Entropy from the von Neumann Algebra of Double-Scaled SYK & Its Connection with Krylov Complexity
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arXiv:2511.03779v2 Announce Type: replace-cross Abstract: We investigate entanglement entropy between the pair of type II$_1$ algebras of the double-scaled SYK (DSSYK) model given a chord state, its holographic interpretation as generalized horizon entropy; particularly in the (anti-)de Sitter ((A)dS) space limits of the bulk dual; and its connection with Krylov complexity. The density matrices in this formalism are operators in the algebras, which are specified by the choice of global state; and there exists a trace to evaluate their von Neumann entropy since the algebras are commutants of each other, which leads to a notion of algebraic entanglement entropy. We match it in triple-scaling limits to an area computed through a Ryu-Takayanagi formula in (A)dS$_2$ space with entangling surfaces at the asymptotic timelike or spacelike boundaries respectively; providing a first-principles example of holographic entanglement entropy for (A)dS$_2$ space. This result reproduces the Bekenstein-Hawking and Gibbons-Hawking entropy formulas for specific entangling regions points, while it decreases for others. This construction does not display some of the puzzling features in dS holography. The entanglement entropy remains real-valued since the theory is unitary, and it depends on the Krylov spread complexity of the Hartle-Hawking state. At last, we discuss higher dimensional extensions.
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https://arxiv.org/abs/2511.03779
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Academic Papers
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svg
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b6fad4bfb3359f5334bf705cc192a89446c3431a1c55c98e508dbb7355f9e328
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2026-01-21T00:00:00-05:00
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Affine Symmetry and the Group-Theoretic Basis of the Unruh Effect
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arXiv:2512.22648v2 Announce Type: replace-cross Abstract: A massless scalar field in two spacetime dimensions splits into two independent sectors of left and right-moving modes on the light cone. At the quantum level, these two sectors carry a representation of the group of affine transformations of the real line, with translations corresponding to transformations generated by light-cone momenta and dilations given by light-cone Rindler momenta formed by a linear combination of generators of boosts and dilations. One-particle states for inertial observers are eigenvectors of translation generators belonging to irreducible representations of the affine group. Rindler one-particle states are related to eigenfunctions of the generator of dilations. We show that simple manipulations connecting these two representations involving the Mellin transform can be used to derive the thermal spectrum of Rindler particles observed by an accelerated observer. Beyond providing a representation-theoretic basis for vacuum thermal effects, our results suggest that analogous phenomena may arise in any quantum system admitting realizations of translation and dilation eigenstates.
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https://arxiv.org/abs/2512.22648
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Academic Papers
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svg
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15d9b3d07817f41e34a8a40ea2cc66c91c8963663d9d1450887cbfac78138511
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2026-01-21T00:00:00-05:00
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Construction of asymptotic quantum many-body scar states in the SU($N$) Hubbard model
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arXiv:2601.04640v2 Announce Type: replace-cross Abstract: We construct asymptotic quantum many-body scars (AQMBS) in one-dimensional SU($N$) Hubbard chains ($N\geq 3$) by embedding the scar subspace into an auxiliary Hilbert subspace $\mathcal{H}_P$ and identifying a parent Hamiltonian within it, together with a corresponding extension of the restricted spectrum-generating algebra to the multi-ladder case. Unlike previous applications of the parent-Hamiltonian scheme, we show that the parent Hamiltonian becomes the SU($N$) ferromagnetic Heisenberg model rather than the spin-1/2 case, so that its gapless magnons realize explicit AQMBS of the original model. Working in the doublon-holon subspace, we derive this mapping, obtain the one-magnon dispersion for periodic and open boundaries, and prove (i) orthogonality to the tower of scar states, (ii) vanishing energy variance in the thermodynamic limit, and (iii) subvolume entanglement entropy with rigorous MPS/MPO bounds. Our results broaden the parent-Hamiltonian family for AQMBS beyond spin-1/2 and provide analytic, low-entanglement excitations in SU($N$)-symmetric systems.
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https://arxiv.org/abs/2601.04640
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Academic Papers
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svg
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6a3cb074c8b5a0a490f8e719b07df1498414f7f1ec911c3220594b6fd5a50a34
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2026-01-21T04:35:42+00:00
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Gold hits record as Trump heads to Davos for Greenland talks
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President en route to World Economic Forum in new plane after electrical problems forced Air Force One to turn back
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https://www.ft.com/content/1369a45e-e39b-4aaa-a347-b1800da7fd31
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Business & Finance
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1f324db0beca2b5e6dd120b60a37ee8aa03b8eaa6a626fb6e4ae5895022d63d9
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2026-01-21T10:55:46+00:00
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Howard Lutnick heckled at World Economic Forum dinner
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Event hosted by Larry Fink descended into uproar after combative remarks from US commerce secretary
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https://www.ft.com/content/e2ae0417-6146-4428-96db-0484a6b024d1
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Business & Finance
| |
34c7b244120e9a0b5be103978bb76dce1fe478bfe0ceb75364c0895e0f45d661
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2026-01-21T05:00:31+00:00
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Trump row over Greenland derails Ukraine postwar deal
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Signature of ‘prosperity plan’ expected at Davos has been postponed amid transatlantic rift
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https://www.ft.com/content/9904baa7-d90b-4170-898d-d5ac8bebe466
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Business & Finance
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