Soft decoding for quantum LDPC codes with experimental validation
Abstract
The decoder is a critical component of a fault-tolerant quantum computer, computing corrections based on parity-check measurements performed throughout the computation. A soft decoder supplements its output with a confidence score which, when used alongside post-selection, can substantially improve logical performance. We introduce a soft beam search decoder for quantum low-density parity-check codes that uses internal decoder data as a confidence metric, removing the need for extra computation. We perform circuit-level simulations of five quantum LDPC codes relevant for superconducting and trapped ion architectures equipped with our global soft decoder and we obtain up to 580× logical-error suppression at a physical error rate of 10−3 while rejecting only 0.1% of shots. Then, we simulate an error detected measurement, which is a core logical operation of the walking cat architecture, using a streaming version of soft beam decoder and we achieve up to 210× error suppression while increasing the rejection probability by only $0.5$ percentage points. Finally, we revisit recent quantum LDPC code memory experiments on trapped ions, demonstrating that our soft decoder doubles the logical qubit lifetimes at the price of a mean rejection rate of 2.6%--5.6% per syndrome round, bringing all five codes into the beyond-breakeven regime.
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BibTeX
@misc{aydin2026soft,
title = {{Soft decoding for quantum LDPC codes with experimental validation}},
author = {Arda Aydin and Edwin Tham and Nicolas Delfosse and Min Ye},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.26958},
eprint = {2609.26958},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.26958},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Soft decoding for quantum LDPC codes with experimental validation
AU - Arda Aydin
AU - Edwin Tham
AU - Nicolas Delfosse
AU - Min Ye
PY - 2026
DA - 2026/09/22
PB - arXiv
DO - 10.48550/arxiv.2609.26958
UR - https://arxiv.org/abs/2609.26958
AB - The decoder is a critical component of a fault-tolerant quantum computer, computing corrections based on parity-check measurements performed throughout the computation. A soft decoder supplements its output with a confidence score which, when used alongside post-selection, can substantially improve logical performance. We introduce a soft beam search decoder for quantum low-density parity-check codes that uses internal decoder data as a confidence metric, removing the need for extra computation. We perform circuit-level simulations of five quantum LDPC codes relevant for superconducting and trapped ion architectures equipped with our global soft decoder and we obtain up to 580× logical-error suppression at a physical error rate of 10^−3 while rejecting only 0.1% of shots. Then, we simulate an error detected measurement, which is a core logical operation of the walking cat architecture, using a streaming version of soft beam decoder and we achieve up to 210× error suppression while increasing the rejection probability by only $0.5$ percentage points. Finally, we revisit recent quantum LDPC code memory experiments on trapped ions, demonstrating that our soft decoder doubles the logical qubit lifetimes at the price of a mean rejection rate of 2.6%--5.6% per syndrome round, bringing all five codes into the beyond-breakeven regime.
ER -