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arXiv:2509.11370 · PRX Intelligence

Neural Decoders for Universal Quantum Algorithms

J. Pablo Bonilla Ataides, Andi Gu, Susanne F. Yelin, Mikhail D. Lukin

Published Jul 28, 2026• 4 citations
arXivHTMLPDF

Abstract

Fault-tolerant quantum computing demands decoders that are fast, accurate, and adaptable to circuit structure and realistic noise. While machine learning decoders have demonstrated impressive performance for quantum memory, their use in algorithmic decoding—where logical gates create complex error correlations—remains limited. We introduce a modular attention-based neural decoder that learns gate-induced correlations and generalizes from training on random circuits to unseen multiqubit algorithmic workloads. Our decoders achieve fast inference and logical error rates comparable to most-likely-error decoders across varied circuit depths and qubit counts. Addressing realistic noise, we incorporate loss-resolving readout, yielding substantial gains when qubit loss is present. We further show that by tailoring the decoder to the structure of the algorithm and decoding only the relevant observables, we can simplify the decoder design without sacrificing accuracy. We validate our framework on multiple error correction codes—including surface codes and two-dimensional color codes—and demonstrate state-of-the-art performance under circuit-level noise. Finally, we show that the attention mechanism learns to track physically meaningful error correlations, consistent with the expected propagation pathways through entangling gates. Enabling experimental validation of deep-circuit fault-tolerant algorithms and architectures [Bluvstein , ], these results establish neural decoders as practical, versatile, and high-performance tools for quantum computing.

DOI
10.1103/vjn1-mbxl

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Fault-tolerant quantum computing demands decoders that are fast, accurate, and adaptable to circuit structure and realistic noise. While machine learning decoders have demonstrated impressive performance for quantum memory, their use in algorithmic decoding—where logical gates create complex error correlations—remains limited. We introduce a modular attention-based neural decoder that learns gate-induced correlations and generalizes from training on random circuits to unseen multiqubit algorithmic workloads. Our decoders achieve fast inference and logical error rates comparable to most-likely-error decoders across varied circuit depths and qubit counts. Addressing realistic noise, we incorporate loss-resolving readout, yielding substantial gains when qubit loss is present. We further show that by tailoring the decoder to the structure of the algorithm and decoding only the relevant observables, we can simplify the decoder design without sacrificing accuracy. We validate our framework on multiple error correction codes—including surface codes and two-dimensional color codes—and demonstrate state-of-the-art performance under circuit-level noise. Finally, we show that the attention mechanism learns to track physically meaningful error correlations, consistent with the expected propagation pathways through entangling gates. Enabling experimental validation of deep-circuit fault-tolerant algorithms and architectures [Bluvstein , ], these results establish neural decoders as practical, versatile, and high-performance tools for quantum computing.
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Abstract Finding efficient decoders for quantum error correcting codes adapted to realistic experimental noise in fault-tolerant devices represents a significant challenge. In this paper we introduce several decoding algorithms complemented by deep neural decoders (DND) and apply them to analyze several fault-tolerant error correction (EC) protocols such as the surface code as well as Steane and Knill EC. Our methods require no knowledge of the underlying noise model afflicting the quantum device making them appealing for real-world experiments. Our analysis is based on a full circuit-level noise model. It considers both distance-three and five codes, and is performed near the codes pseudo-threshold regime. Training DND in low noise rate regimes appears to be a challenging machine learning endeavour. We provide a detailed description of our neural network architectures and training methodology. We then discuss both the advantages and limitations of DND. Lastly, we provide a rigorous analysis of the decoding runtime of trained DND and compare our methods with anticipated gate times in future quantum devices. Given the broad applications of our decoding schemes, we believe that the methods presented in this paper could have practical applications for near term fault-tolerant experiments.
The practical realization of fault-tolerant quantum computing critically hinges on the capacity of quantum error correction (QEC) schemes to robustly mitigate physical noise. Among the foremost candidates, the surface code is distinguished by its high threshold and local stabilizer checks. In recent years, neural network-based decoders, particularly those leveraging deep reinforcement learning (RL) and convolutional architectures, have demonstrated competitive performance against algorithmic staples such as Minimum Weight Perfect Matching (MWPM) and Union-Find. However, the vast majority of these learned decoders are trained and evaluated under idealized phenomenological or circuit-level depolarizing noise models. Real-world quantum processors exhibit complex, compound noise profiles encompassing crosstalk, leakage, non-Markovian temporal drift, and spatially correlated errors. In this work, we empirically evaluate the robustness of state-of-the-art neural decoders against highly structured compound noise models. We introduce a comprehensive stress-testing methodology tailored to quantify the degradation of the logical error rate when decoders are subjected to out-of-distribution noise characteristics. Our empirical results reveal that while neural decoders can overfit to their training noise profile, strategically designed training curricula and architecture regularizations enable significant resilience. We provide extensive numerical benchmarks validating that learned decoders can maintain near-optimal pseudothresholds across a broad spectrum of shifting noise conditions, highlighting their readiness for real-world superconducting qubit deployments.
Fault-tolerant quantum computing will require error rates far below those achievable with physical qubits. Quantum error correction (QEC) bridges this gap, but depends on decoders being simultaneously fast, accurate, and scalable. This combination of requirements remains unmet by a machine-learning decoder, nor by any decoder for promising resource-efficient codes such as the color code. Here we introduce AlphaQubit 2, a neural-network decoder that achieves near-optimal logical error rates for both surface and color codes at scale under realistic noise. For the color code, it is orders of magnitude faster than other high-accuracy decoders. We demonstrate real-time decoding faster than 1μs per cycle on commercial accelerators: for the surface code to distance 11, with better accuracy than leading real-time decoders; and the first real-time decoding of the color code to distance 9. These results support the practical application of a wider class of promising QEC codes, and establish a credible path towards high-accuracy, real-time neural decoding at the scales required for fault-tolerant quantum computation.
The practical realization of fault-tolerant quantum computing critically hinges on the capacity of quantum error correction (QEC) schemes to robustly mitigate physical noise. Among the foremost candidates, the surface code is distinguished by its high threshold and local stabilizer checks. In recent years, neural network-based decoders, particularly those leveraging deep reinforcement learning (RL) and convolutional architectures, have demonstrated competitive performance against algorithmic staples such as Minimum Weight Perfect Matching (MWPM) and Union-Find. However, the vast majority of these learned decoders are trained and evaluated under idealized phenomenological or circuit-level depolarizing noise models. Real-world quantum processors exhibit complex, compound noise profiles encompassing crosstalk, leakage, non-Markovian temporal drift, and spatially correlated errors. In this work, we empirically evaluate the robustness of state-of-the-art neural decoders against highly structured compound noise models. We introduce a comprehensive stress-testing methodology tailored to quantify the degradation of the logical error rate when decoders are subjected to out-of-distribution noise characteristics. Our empirical results reveal that while neural decoders can overfit to their training noise profile, strategically designed training curricula and architecture regularizations enable significant resilience. We provide extensive numerical benchmarks validating that learned decoders can maintain near-optimal pseudothresholds across a broad spectrum of shifting noise conditions, highlighting their readiness for real-world superconducting qubit deployments.
As quantum hardware advances toward enabling error-corrected quantum circuits in the near future, the absence of an efficient polynomial-time decoding algorithm for logical circuits presents a critical bottleneck. While quantum memory decoding has been well studied, inevitable correlated errors introduced by transversal entangling logical gates prevent the straightforward generalization of quantum memory decoders. Here we introduce a data-centric, modular decoder framework, the Multi-Core Circuit Decoder (MCCD), which consists of decoder modules corresponding to each logical operation supported by the quantum hardware. The MCCD handles both single-qubit and entangling gates within a unified framework. We train MCCD using mirror-symmetric random Clifford circuits, demonstrating its ability to effectively learn correlated decoding patterns. Through extensive testing on circuits substantially deeper than those used in training, we show that MCCD maintains high logical accuracy while exhibiting competitive polynomial decoding time across increasing circuit depths and code distances. When compared with conventional decoders such as minimum weight perfect matching (MWPM), most likely error (MLE) and belief propagation with ordered statistics post-processing (BP-OSD), MCCD achieves competitive accuracy with substantially better time efficiency, particularly for circuits with entangling gates. Our approach provides a noise-model-agnostic solution to the decoding challenge in deep logical quantum circuits.