利用么正性基准估计量子信道中的相关性和不可分离性
Estimation of correlations and non-separability in quantum channels via unitarity benchmarking
摘要：
在系统之间传输相干量子信息的能力是量子技术的基本组成部分，并导致全局量子过程中的相干关联。然而，相对于量子态，量子信道中的关联结构研究较少。最近的技术在随机基准的激励下，我们开发了一系列的结果，有效地估计相关性的二分量子信道。我们引入子酉措施，是不变的基础上的局部变化，推广的渠道的酉性，并允许通道内的相干信息交换的分析。利用这些，我们表明，酉是一夫一妻制，并提供了一个新的信息干扰关系。然后，我们定义了一个概念的相关么正性，量化的相关性在一个给定的通道。最重要的是，我们表明，这一措施是严格有界的可分通道的集合，因此提供了一个见证的不可分性。最后，我们描述了如何有效的噪声信道的措施，可以有效地估计在不同的随机基准测试协议。我们发现，相关的么正性可以估计在任何可分离的量子信道的SPAM鲁棒的方式，并表明，基准/断层扫描协议与中间电路复位可以可靠地见证足够小的复位错误的不可分离性。我们开发的工具提供的信息超出了通过同步随机基准测试获得的信息，因此可以应用于量子设备中的串扰和相干误差的分析。
英文摘要：
The ability to transfer coherent quantum information between systems is a fundamental component of quantum technologies and leads to coherent correlations within the global quantum process. However correlation structures in quantum channels are less studied than those in quantum states. Motivated by recent techniques in randomized benchmarking, we develop a range of results for efficient estimation of correlations within a bipartite quantum channel. We introduce sub-unitarity measures that are invariant under local changes of basis, generalize the unitarity of a channel, and allow for the analysis of coherent information exchange within channels. Using these, we show that unitarity is monogamous, and provide a novel information-disturbance relation. We then define a notion of correlated unitarity that quantifies the correlations within a given channel. Crucially, we show that this measure is strictly bounded on the set of separable channels and therefore provides a witness of non-separability. Finally, we describe how such measures for effective noise channels can be efficiently estimated within different randomized benchmarking protocols. We find that the correlated unitarity can be estimated in a SPAM-robust manner for any separable quantum channel, and show that a benchmarking/tomography protocol with mid-circuit resets can reliably witness non-separability for sufficiently small reset errors. The tools we develop provide information beyond that obtained via simultaneous randomized benchmarking and so could find application in the analysis of cross-talk and coherent errors in quantum devices.
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