Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
CAPSS, Physics Department, Bose Institute, Salt Lake, Sector V, Kolkata 700097, India.
Phys Rev Lett. 2018 May 25;120(21):210402. doi: 10.1103/PhysRevLett.120.210402.
Can the most "classical-like" of all quantum states, namely the Schrödinger coherent state of a harmonic oscillator, exhibit nonclassical behavior? We find that for an oscillating object initially in a coherent state, merely by observing at various instants which spatial region the object is in, the Leggett-Garg inequality (LGI) can be violated through a genuine negative result measurement, thereby repudiating the everyday notion of macrorealism. This violation thus reveals an unnoticed nonclassicality of the very state which epitomizes classicality within the quantum description. It is found that for any given mass and oscillator frequency, a significant quantum violation of LGI can be obtained by suitably choosing the initial peak momentum of the coherent state wave packet. It thus opens up potentially the simplest way (without coupling with any ancillary quantum system or using nonlinearity) for testing whether various recently engineered and sought after macroscopic oscillators, such as feedback cooled thermal trapped nanocrystals of ∼10^{6}-10^{9} amu mass, are indeed bona fide nonclassical objects.
最“经典”的量子态，即谐振子的薛定谔相干态，是否能表现出非经典行为？我们发现，对于初始处于相干态的振动物体，仅仅通过在不同时刻观察物体所在的空间区域，就可以通过真正的负结果测量违反莱格特-加尔加不等式（LGI），从而否定宏观现实的日常概念。这种违反行为揭示了在量子描述中代表经典性的状态中存在一种未被注意到的非经典性。研究发现，对于给定的质量和振荡器频率，通过适当选择相干态波包的初始峰值动量，可以获得显著的 LGI 量子违反。因此，它为测试各种最近设计和追求的宏观振荡器（如反馈冷却热捕获的纳米晶体，质量约为 10^6-10^9amu）是否确实是真正的非经典物体，提供了一种最简单的方法（无需与任何辅助量子系统耦合或使用非线性）。
