AI 中文总结
本文研究噪声量子体积采样中去极化噪声、二分负性纠缠与重输出概率的权衡，发现有限尺寸效应下NISQ计算机可过量子体积阈值却无全局纠缠。
AI 中文摘要
量子体积协议利用随机 scrambling 电路对含噪声中等规模量子（NISQ）计算机进行基准测试。量子体积作为小型含噪声量子计算机的基准被广泛认可，它要求量子计算机在方形电路中实现大量非局域纠缠门，这激励硬件具备高量子比特数、长量子比特相干时间和所有门低错误率。量子体积电路固有地产生高纠缠态，该态对错误和退相干脆弱。量子体积基准测量名为重输出概率（HOP）的可观测量，其中 HOP 为 $0.5$ 对应完全退相干，对于完全相干量子处理器，系统尺寸极限下 HOP 约为 $0.84$。本文数值研究量子体积电路中去极化噪声、以二分负性度量量化的纠缠以及 HOP 之间的权衡关系。研究结果阐释了先前量子计算机上小规模量子体积演示的背景，并强调在去极化噪声下，由于有限系统尺寸效应，重输出概率可大于 $0.5$，而二分负性纠缠已被破坏。这意味着，尽管可能性低，NISQ 计算机可通过量子体积基准测试的 $2/3$ 阈值，而底层量子计算无全局纠缠——尽管仅适用于小 $n$。
英文摘要
The Quantum Volume protocol uses scrambling random circuits to benchmark NISQ computers. Quantum Volume is generally well-regarded as a benchmark for small, noisy, quantum computers because it requires the quantum computer to implement many non-local entangling gates within a square-shaped circuit, which incentivizes high qubit count, long qubit coherence times, and low error rates on all hardware gates. Quantum Volume circuits inherently produce high-entanglement states that are fragile to errors and decoherence. The Quantum Volume benchmark measures an observable called heavy-output-probability (HOP), where an HOP of $0.5$ corresponds to complete loss of coherence, and in the limit of system size an HOP $\approx 0.84$ for a fully coherent quantum processor. Here, we numerically study the tradeoff between depolarizing noise, entanglement as quantified by the bipartite negativity measure, and HOP in quantum volume circuits. Our results contextualize prior small scale quantum volume demonstrations on quantum computers and highlight that under depolarizing noise, due to finite system size effects heavy output probabilities can be greater than $0.5$ while the bipartite negativity entanglement has been destroyed. This implies, although improbable, that a NISQ computer could pass the Quantum Volume benchmark test threshold of $2/3$ while the underlying quantum computation has no global entanglement -- albeit only for small $n$.
