标题： 可扩展交叉熵基准测试的实验演示：用于检测超导量子处理器中的测量诱导相变 显示英文标题

标题： Experimental demonstration of scalable cross-entropy benchmarking to detect measurement-induced phase transitions on a superconducting quantum processor

摘要： 受随机幺正演化和时空随机点测量的量子系统表现出依赖于这些测量频率的纠缠相变。过去的研究已经在近期量子计算机上实验观察到了纠缠相变，但由于量子态层析和后选择的指数开销，使用纠缠熵的方法不具备可扩展性。最近，提出了一种替代协议，利用线性交叉熵来检测纠缠相变，试图消除这两个瓶颈。 在这里，我们报告了在IBM量子硬件上最多22个量子比特的一维和全连接系统中对该协议的演示，这一领域目前若需要后选择则无法访问。我们展示了数据在半定量符合理论的临界指数下坍缩到尺度函数上。 我们对交叉熵基准(XEB)协议的演示为研究更大规模近期量子系统中的测量诱导纠缠相变及相关临界现象铺平了道路。 显示英文摘要

摘要： Quantum systems subject to random unitary evolution and measurements at random points in spacetime exhibit entanglement phase transitions which depend on the frequency of these measurements. Past work has experimentally observed entanglement phase transitions on near-term quantum computers, but the characterization approach using entanglement entropy is not scalable due to exponential overhead of quantum state tomography and postselection. Recently, an alternative protocol to detect entanglement phase transitions using linear cross entropy was proposed, attempting to eliminate both bottlenecks. Here, we report demonstrations of this protocol in systems with one-dimensional and all-to-all connectivities on IBM's quantum hardware on up to 22 qubits, a regime which is presently inaccessible if postselection is required. We demonstrate data collapses onto scaling functions with critical exponents in semiquantitative agreement with theory. Our demonstration of the cross entropy benchmark (XEB) protocol paves the way for studies of measurement-induced entanglement phase transitions and associated critical phenomena on larger near-term quantum systems.