本期文章：《自然》：Online/在线发表
近日，谷歌量子人工智能和合作者研究团队取得一项新进展。他们实现了表面代码阈值以下的量子纠错。相关研究成果已于2024年12月9日在国际权威学术期刊《自然》上发表。
量子纠错通过将多个物理量子比特组合成一个逻辑量子比特，为实现实用化量子计算提供了途径，其中随着量子比特数量的增加，逻辑错误率会呈指数级下降。然而，这种指数级抑制仅在物理错误率低于某个临界阈值时才会发生。
该研究团队展示了在最新一代的超导处理器Willow上实现的两个低于阈值的表面码存储器：一个是距离-7码，另一个是与实时解码器集成的距离-5码。当研究人员将码距增加两倍时，更大的量子存储器的逻辑错误率被抑制了2.14±0.02倍，最终实现了一个101量子比特的距离-7码，每轮错误校正的错误率为0.143% ± 0.003%。
这个逻辑存储器的性能也超过了盈亏平衡点，其最佳物理量子比特寿命提高了2.4±0.3倍。该研究的系统在实时解码时保持了低于阈值的性能，在距离-5码下，解码器的平均延迟为63微秒，可持续高达一百万个周期，每个周期时间为1.1微秒。
研究人员还运行了距离高达29的重复码，并发现逻辑性能受到罕见相关错误事件的限制，这些事件大约每小时发生一次，即每3×109个周期发生一次。这项研究结果表明，如果进行扩展，器件性能可以满足大规模容错量子算法的运行要求。
附：英文原文
Title: Quantum error correction below the surface code threshold
Author: Google Quantum AI and Collaborators
Issue&Volume: 2024-12-09
Abstract: Quantum error correction [1, 2, 3, 4] provides a path to reach practical quantum computing by combining multiple physical qubits into a logical qubit, where the logical error rate is suppressed exponentially as more qubits are added. However, this exponential suppression only occurs if the physical error rate is below a critical threshold. Here, we present two below-threshold surface code memories on our newest generation of superconducting processors, Willow: a distance-7 code, and a distance-5 code integrated with a real-time decoder. The logical error rate of our larger quantum memory is suppressed by a factor of 2.14±0.02 when increasing the code distance by two, culminating in a 101-qubit distance-7 code with 0.143% ± 0.003% error per cycle of error correction. This logical memory is also beyond break-even, exceeding its best physical qubit’s lifetime by a factor of 2.4±0.3. Our system maintains below-threshold performance when decoding in real time, achieving an average decoder latency of 63 μs at distance-5 up to a million cycles, with a cycle time of 1.1 μs. We also run repetition codes up to distance-29 and find that logical performance is limited by rare correlated error events occurring approximately once every hour, or 3×109 cycles. Our results present device performance that, if scaled, could realize the operational requirements of large scale fault-tolerant quantum algorithms.
DOI: 10.1038/s41586-024-08449-y
Source: https://www.nature.com/articles/s41586-024-08449-y
期刊信息
Nature：《自然》，创刊于1869年。隶属于施普林格·自然出版集团，最新IF：69.504
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