docs/index.md

# Dense-Evolution

**Dense statevector quantum simulator · JAX XLA · NISQ · VQE · QML**

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Dense-Evolution is a high-performance statevector simulator for deep NISQ circuits, VQE
pipelines, and QML workloads. It eliminates Kronecker-product overhead via stride-sliced
linear kernel fusion compiled through JAX XLA, keeping memory at the theoretical minimum
of `2ⁿ × 16 bytes`.

## What's in here

- **[`DenseSVSimulator`](api/simulator.md)** — the core dense statevector engine, JIT-fused
  circuit execution, projective measurement.
- **[`MPSSimulator`](api/mps.md)** — matrix-product-state engine for low-entanglement
  circuits at hundreds of qubits, with a `jax.lax.scan`-fused execution path.
- **[`Chunk`](api/chunk.md)** — anti-OOM statevector chunking for circuits too large for a
  single dense allocation, including a real multi-device distributed dispatch path.
- **[`QASMParser`](api/parser.md)** — OpenQASM 2.0 / 3.0 parsing, including `for` loops,
  range syntax, and QASM3 classical `bit` registers.
- **[`dense_evolution.mitigation`](api/mitigation.md)** — Zero-Noise Extrapolation, both the
  classic scalar/vector form and a density-matrix extension (Smolin-Gambetta-Smith physical
  projection, Uhlmann fidelity), every entry point with a `jax.jit`-compatible variant.
- **[`dense_evolution.healing`](api/healing.md)** — the predictive-healing primitives
  (`calculate_delta_preemp`, `calculate_vettore_dinamico`, ...) ZNE's healing-adapted branch
  is built on.
- **[`NoiseModel`](api/registry.md)** — Kraus-channel noise (depolarizing, bitflip,
  phaseflip, amplitude damping, and a combined worst-case model), JAX- and NumPy-native.
- **Interop** with [Qiskit and PennyLane](api/interop.md), and [autodiff](api/autodiff.md)
  through `circuit_to_energy_fn` for gradient-based VQE.

## Module dependencies

Real module graph, traced from the actual `import` statements in each file (not an
idealized layering) -- circuit sources feed three interchangeable execution engines, which
in turn feed the higher-level mitigation/autodiff layers.

```mermaid
flowchart LR
    subgraph core["Core"]
        parser["parser<br/>(QASMParser)"]
        gates["gates"]
        registry["registry<br/>(NoiseModel)"]
        compiler["compiler<br/>(QuantumTranspiler)"]
    end

    subgraph engines["Engines"]
        simulator["simulator<br/>(DenseSVSimulator)"]
        mps["mps<br/>(MPSSimulator)"]
        chunk["chunk<br/>(Chunk)"]
    end

    subgraph higher["Higher-level"]
        interop["interop<br/>(Qiskit / PennyLane)"]
        autodiff["autodiff<br/>(circuit_to_energy_fn)"]
        healing["healing<br/>(predictive primitives)"]
        mitigation["mitigation<br/>(ZNE)"]
    end

    gates --> registry
    simulator --> registry
    simulator --> gates
    simulator --> compiler
    mps --> compiler
    mps --> gates
    chunk --> simulator
    chunk --> compiler
    chunk --> gates
    interop --> parser
    interop --> simulator
    autodiff --> parser
    autodiff --> gates
    autodiff --> compiler
    autodiff --> registry
    mitigation --> healing
```

## Where to start

New to the package? Start with **[Getting Started](getting-started.md)**.

Looking for a specific function or class? Jump straight to the **[API
Reference](api/index.md)**.

Want to see what changed recently? Check the **[Changelog](changelog.md)**.

## Honesty as a design principle

This library's docstrings and changelog document real, measured findings — including
negative results and rejected approaches — not just the features that worked. Where a
number is quoted (a speedup, a fidelity improvement, a coverage percentage), it was
measured directly and the measurement is described, not assumed. See the
[Changelog](changelog.md) for the full history.