Decoder Switching: Breaking the Speed-Accuracy Tradeoff in Real-Time Quantum Error Correction

TL;DR

This paper introduces a decoder switching framework for quantum error correction that combines speed and accuracy, enabling real-time decoding without sacrificing performance, thus overcoming a fundamental speed-accuracy trade-off.

Contribution

The paper proposes a novel decoder switching approach and an online decoding scheme that balance decoding speed and accuracy in quantum error correction.

Findings

Achieves high accuracy with decoding times comparable to fast decoders

Surpasses the accuracy of the fast decoder using the switching framework

Prevents exponential slowdown in quantum computation through criteria for decoder switching

Abstract

The realization of fault-tolerant quantum computers hinges on the construction of high-speed, high-accuracy, real-time decoding systems. The persistent challenge lies in the fundamental trade-off between speed and accuracy: efforts to improve the decoder's accuracy often lead to unacceptable increases in decoding time and hardware complexity, while attempts to accelerate decoding result in a significant degradation in logical error rate. To overcome this challenge, we propose a novel framework, decoder switching, which balances these competing demands by combining a faster, soft-output decoder ("weak decoder") with a slower, high-accuracy decoder ("strong decoder"). In usual rounds, the weak decoder processes error syndromes and simultaneously evaluates its reliability via soft information. Only when encountering a decoding window with low reliability do we switch to the strong decoder to achieve more accurate decoding. Numerical simulations suggest that this framework can achieve accuracy comparable to, or even surpassing, that of the strong decoder, while maintaining an average decoding time on par with the weak decoder. We also develop an online decoding scheme tailored to our framework, named double window decoding, and elucidate the criteria for preventing an exponential slowdown of quantum computation. These findings break the long-standing speed-accuracy trade-off, paving the way for scalable real-time decoding devices.