Kamakari Hirsh, Sun Jiace, Li Yaodong, Thio Jonathan J, Gujarati Tanvi P, Fisher Matthew P A, Motta Mario, Minnich Austin J
California Institute of Technology, Division of Engineering and Applied Science, Pasadena, CA 91125, USA.
Stanford University, Department of Physics, Stanford, California 94305, USA.
Phys Rev Lett. 2025 Mar 28;134(12):120401. doi: 10.1103/PhysRevLett.134.120401.
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.
受随机酉演化及时空随机点处测量影响的量子系统会展现出依赖于这些测量频率的纠缠相变。过去的工作已在近期量子计算机上通过实验观测到了纠缠相变，但由于量子态层析成像和后选择的指数级开销，使用纠缠熵的表征方法不可扩展。最近，有人提出了一种使用线性交叉熵来检测纠缠相变的替代协议，试图消除这两个瓶颈。在此，我们报告了在IBM量子硬件上具有一维和全对全连接性的系统中，针对多达22个量子比特的该协议的演示，这是一个如果需要后选择目前无法实现的区域。我们展示了数据塌缩到具有临界指数的标度函数上，与理论半定量相符。我们对交叉熵基准（XEB）协议的演示为在更大的近期量子系统上研究测量诱导的纠缠相变及相关临界现象铺平了道路。
