During a quantum measurement, superpositions of states with different observable properties probabilistically collapse into one with a sharp value of the measured observable. In macroscopic quantum systems, this collapse arises via a continuous measurement-induced phase transition (MIPT) at a critical value of the strength of interaction with the measurement apparatus. MIPTs lie outside established paradigms for equilibrium or nonequilibrium critical phenomena and delineate distinct, stable dynamical and computational phases of matter. Quantum computers enable programmable simulation of the interaction of a measurement apparatus with a dynamical quantum system, to explore MIPT phenomena over a range of system sizes while retaining quantum coherence. Yet, existing experimental protocols rely on fundamentally nonscalable postselection techniques or direct classical simulation of quantum circuits. Here, we report the scalable observation of finite-size scaling evidence for an observable-sharpening MIPT in monitored quantum circuits in a chain of Yb+171 ions in Quantinuum’s H1-1 trapped-ion quantum processor. By leveraging an equivalent description as a statistical physics problem, we implement scalable classical algorithms to infer the value of the measured observable from a single experimental shot. This technique enables a truly scalable protocol to observe observable-sharpening MIPTs in generic classes of circuits that cannot be directly classically simulated and also provides enhanced means to detect and suppress errors in the quantum simulation. Published by the American Physical Society 2024

中文翻译：

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将量子测量坍缩观察为可学习性相变


在量子测量过程中，具有不同可观察对象属性的状态叠加概率性地坍缩成一个状态，其测量值为尖锐的可观察对象。在宏观量子系统中，这种坍缩是通过连续测量诱导相变 （MIPT） 在与测量设备相互作用强度的临界值处产生的。MIPT 位于平衡或非平衡临界现象的既定范式之外，描绘了物质独特、稳定的动力学和计算阶段。量子计算机能够对测量设备与动态量子系统的相互作用进行可编程模拟，以在保持量子相干性的同时探索一系列系统大小的 MIPT 现象。然而，现有的实验方案依赖于根本上不可扩展的后选择技术或量子电路的直接经典模拟。在这里，我们报告了在 Quantinuum 的 H1-1 囚禁离子量子处理器的 Yb+171 离子链中受监控的量子电路中可观察锐化 MIPT 的有限尺寸缩放证据的可扩展观察。通过利用等效描述作为统计物理问题，我们实现了可扩展的经典算法，以从单个实验镜头中推断出被测可观测值。该技术使真正可扩展的协议能够观察无法直接经典模拟的通用电路类中的可观察锐化 MIPT，并且还提供了增强的方法来检测和抑制量子模拟中的错误。 美国物理学会 2024 年出版