---
library_name: ising-decoding
tags:
  - quantum
  - qec
  - error_correction
  - decoders
  - surface_code
  - predecoder
license: apache-2.0
---

# Quantispect Overview

![Quantispect Neural Pre-Decoder Architecture](framework.png)

## Model Summary

| Item | Value |
|---|---:|
| Model name | Quantispect |
| Checkpoint file | `Quantispect_RF13_v1.0.10.pt` |
| Total parameters | ~0.663M |
| Checkpoint size | ~2.63 MB |
| Architecture | FastHyper-style 3D CNN neural pre-decoder |
| Receptive field | R=13 |
| Input tensor | `(B, 4, T, D, D)` |
| Output tensor | `(B, 4, T, D, D)` |
| Release date | April 26, 2026 |

## Description:

Quantispect is a compact neural pre-decoder for rotated surface-code quantum error correction. It consumes five-dimensional syndrome volumes across batch, channel, time, and two spatial dimensions, and predicts local correction maps that are consumed by a downstream global decoder such as MWPM / PyMatching or an Ising-decoding post-processing pipeline.

Quantispect is designed to run inside an NVIDIA Ising-Decoding-compatible workflow after applying the Quantispect code patch included with this model release.

## Model Architecture:

Architecture type: 3D Convolutional Neural Network (3D CNN)

Network architecture: custom multi-branch spatio-temporal 3D CNN with residual FastHyper blocks.

### Input

Input shape:

```text
(B, 4, T, D, D)
```

### Stem

```text
Conv3D 4 -> 96, kernel 3x3x3
GroupNorm
GELU
```

Stem output shape:

```text
(B, 96, T, D, D)
```

### Main Body

The main body contains five repeated `FastHyperBlock` modules:

```text
FastHyperBlock x5
```

Each `FastHyperBlock` first expands the feature width from 96 to 144 channels with a 1x1x1 convolution, then applies three parallel feature extraction branches:

```text
Pre-projection: GroupNorm -> 1x1x1 Conv3D, 96 -> 144 -> GELU

Branch A: Depthwise Conv3D, kernel 1x3x3, spatial branch
Branch B: Depthwise Conv3D, kernel 3x1x1, temporal branch
Branch C: GroupNorm -> Grouped Conv3D, kernel 3x3x3, groups=6, joint local spatio-temporal branch
```

The three branch outputs are aligned and fused by element-wise summation rather than channel concatenation. The fused feature is then projected and recalibrated:

```text
Element-wise sum fusion
1x1x1 Conv3D projection, 144 -> 96
GELU
ChannelGate / SE-style channel attention
Dropout3D
Residual connection
```

Main body output shape:

```text
(B, 96, T, D, D)
```

### Head

```text
GroupNorm
1x1x1 Conv3D, 96 -> 96
GELU
1x1x1 Conv3D, 96 -> 4
```

Output shape:

```text
(B, 4, T, D, D)
```

The output maps are used by the residual-syndrome construction module and then passed to MWPM / Ising-decoder post-processing.

## Usage:

Quantispect is intended to be used with the NVIDIA Ising-Decoding environment:

```text
https://github.com/NVIDIA/Ising-Decoding
```

A clean NVIDIA Ising-Decoding checkout does not natively know the Quantispect / FastHyper architecture. To run `Quantispect_RF13_v1.0.10.pt`, first apply the Quantispect code patch included in this model repository.


### Required code patch files

The patch package should preserve the following relative paths:

```text
quantispect_code_patch/
├── conf/
│   └── config_public.yaml
└── code/
    ├── model/
    │   ├── predecoder_fasthyper_rf13_v1.py
    │   ├── factory.py
    │   └── registry.py
    ├── workflows/
    │   ├── config_validator.py
    │   └── run.py
    └── scripts/
        └── local_run.sh
```

These files should be copied into the NVIDIA Ising-Decoding repository with the same relative paths:

```text
conf/config_public.yaml                    -> Ising-Decoding/conf/config_public.yaml
code/model/predecoder_fasthyper_rf13_v1.py -> Ising-Decoding/code/model/predecoder_fasthyper_rf13_v1.py
code/model/factory.py                      -> Ising-Decoding/code/model/factory.py
code/model/registry.py                     -> Ising-Decoding/code/model/registry.py
code/workflows/config_validator.py         -> Ising-Decoding/code/workflows/config_validator.py
code/workflows/run.py                      -> Ising-Decoding/code/workflows/run.py
code/scripts/local_run.sh                  -> Ising-Decoding/code/scripts/local_run.sh
```

The patch mainly adds the `predecoder_fasthyper_rf13_v1` model implementation, registers `model_id: 6`, adds the Quantispect model hyperparameters to `config_public.yaml`, and enables explicit `.pt` checkpoint loading through `model_checkpoint_file`.

### Apply the patch

From the directory containing both the clean NVIDIA Ising-Decoding repository and this downloaded patch package:

```bash
cp -r code/* Ising-Decoding/code/
cp -r conf/* Ising-Decoding/conf/
```

Then place the Quantispect checkpoint under the repository model directory:

```bash
mkdir -p Ising-Decoding/models
cp Quantispect_RF13_v1.0.10.pt Ising-Decoding/models/Quantispect_RF13_v1.0.10.pt
```

Expected directory layout:

```text
Ising-Decoding/
├── code/
│   ├── model/
│   │   └── predecoder_fasthyper_rf13_v1.py
│   ├── workflows/
│   │   ├── config_validator.py
│   │   └── run.py
│   └── scripts/
│       └── local_run.sh
├── conf/
│   └── config_public.yaml
├── models/
│   └── Quantispect_RF13_v1.0.10.pt
└── README.md
```

## Inference Deployment:

Configure the NVIDIA Ising-Decoding repository for inference, apply the Quantispect patch files above, and place the downloaded model checkpoint at `models/Quantispect_RF13_v1.0.10.pt`.

Run from the repository root:

```bash
cd Ising-Decoding

CUDA_VISIBLE_DEVICES=0,1,2,3 \
PYTHONUNBUFFERED=1 \
PYTORCH_CUDA_ALLOC_CONF=expandable_segments:True \
WORKFLOW=inference \
EXPERIMENT_NAME=infer_quantispect \
TORCH_COMPILE=0 \
EXTRA_PARAMS="+model_checkpoint_file=models/Quantispect_RF13_v1.0.10.pt" \
bash code/scripts/local_run.sh \
2>&1 | tee infer_quantispect.log
```