This paper reviews the progress that has been made in our knowledge of quantum correlations at the mesoscopic and macroscopic level. We begin by summarizing the Einstein-Podolsky-Rosen (EPR) argument and the Bell correlations that cannot be explained by local hidden variable theories. It was originally an open question as to whether (and how) such quantum correlations could occur on a macroscopic scale, since this would seem to contradict the correspondence principle. The purpose of this review is to examine how this question has been answered over the decades since the original papers of EPR and Bell. We first review work relating to higher spin measurements which revealed that macroscopic quantum states could exhibit Bell correlations. This covers higher dimensional, multiparticle and continuous-variable EPR and Bell states where measurements on a single system give a spectrum of outcomes, and also multipartite states where measurements are made at multiple separated sites. It appeared that the macroscopic quantum observations were for an increasingly limited span of measurement settings and required a fine resolution of outcomes. Motivated by this, we next review correlations for macroscopic superposition states, and examine predictions for the violation of Leggett-Garg inequalities using dynamical quantum systems. These results reveal Bell correlations for coarse-grained measurements which need only distinguish between macroscopically distinct states, thus bringing into question the validity of certain forms of macroscopic realism. Finally, we review progress for massive systems, including Bose-Einstein condensates and optomechanical oscillators, where EPR-type correlations have been observed between massive systems. Experiments are summarized which support the predictions of quantum mechanics in mesoscopic regimes.

本文回顾了我们在介观和宏观层面上对量子相关性的了解所取得的进展。我们首先总结无法用局部隐变量理论解释的爱因斯坦-波多尔斯基-罗森 (EPR) 论证和贝尔相关性。这种量子关联是否（以及如何）在宏观尺度上发生最初是一个悬而未决的问题，因为这似乎与对应原理相矛盾。本综述的目的是考察自 EPR 和贝尔发表原始论文以来的几十年来如何回答这个问题。我们首先回顾与高自旋测量相关的工作，这些工作揭示了宏观量子态可以表现出贝尔相关性。这涵盖了更高维度，多粒子和连续变量 EPR 和贝尔状态（在单个系统上进行的测量给出一系列结果）以及多部分状态（在多个单独的站点进行测量）。宏观量子观测似乎适用于越来越有限的测量设置范围，并且需要对结果进行精细分辨率。受此启发，我们接下来回顾宏观叠加态的相关性，并使用动态量子系统检查对违反 Leggett-Garg 不等式的预测。这些结果揭示了粗粒度测量的贝尔相关性，只需要区分宏观上不同的状态，从而对某些形式的宏观现实主义的有效性提出了质疑。最后，我们回顾大规模系统的进展，包括玻色-爱因斯坦凝聚体和光机械振荡器，其中在大规模系统之间观察到了 EPR 型相关性。总结了支持介观体系中量子力学预测的实验。