标题： 量子非破坏性测量和莱格特-加尔格不等式 显示英文标题

标题： Quantum Non-Demolition Measurements and Leggett-Garg inequality

摘要： 量子非破坏性测量定义了一种非侵入性协议，用于从目标监测的量子系统中提取信息。 它们利用一个额外的量子系统，该系统依次与目标系统耦合。 最终，通过对附加系统进行测量，我们可以提取关于量子系统动力学相对于特定可观测量所发展的时间关联的信息。 此协议导致被测量可观测量结果的准概率分布，该分布可能是负值。 我们证明了这些负区域的存在是违反宏观实在性条件的必要且充分条件。 这是一个比常用的Leggett-Garg不等式违反更强得多的条件。 事实上，我们展示了存在一些情况，即使宏观实在性条件被违反，Leggett-Garg不等式仍能成立。 因此，量子非破坏性测量协议是一种确定识别系统量子行为的特权工具。 因此，它在从量子性认证到量子-经典过渡研究等多个领域具有广泛的应用。 显示英文摘要

摘要： Quantum non-demolition measurements define a non-invasive protocol to extract information from a quantum system that we aim to monitor. They exploit an additional quantum system that is sequentially coupled to the system. Eventually, by measuring the additional system, we can extract information about temporal correlations developed by the quantum system dynamics with respect to a given observable. This protocol leads to a quasi-probability distribution for the measured observable outcomes, which can be negative. We prove that the presence of these negative regions is a necessary and sufficient condition for the violation of macrorealism. This is a much stronger condition than the violation of the Leggett-Garg inequalities commonly used for the same task. Indeed, we show that there are situations in which Leggett-Garg inequalities are satisfied even if the macrorealism condition is violated. As a consequence, the quantum non-demolition protocol is a privileged tool to identify with certainty the quantum behavior of a system. As such, it has a vast number of applications to different fields from the certification of quantumness to the study of the quantum-to-classical transition.