Bohmann Martin, Agudelo Elizabeth
QSTAR, INO-CNR, and LENS, Largo Enrico Fermi 2, I-50125 Firenze, Italy.
Institute for Quantum Optics and Quantum Information-IQOQI Vienna, Austrian Academy of Sciences, Boltzmanngasse 3, 1090 Vienna, Austria.
Phys Rev Lett. 2020 Apr 3;124(13):133601. doi: 10.1103/PhysRevLett.124.133601.
We derive a family of inequalities involving different phase-space distributions of a quantum state which have to be fulfilled by any classical state. The violation of these inequalities is a clear signature of nonclassicality. Our approach combines the characterization of nonclassical effects via negativities in phase-space distributions with inequality conditions usually being formulated for moments of physical observables. Importantly, the obtained criteria certify nonclassicality even when the involved phase-space distributions are non-negative. Moreover, we show how these inequalities are related to correlation measurements. The strength of the derived conditions is demonstrated by different examples, including squeezed states, lossy single-photon states, and even coherent states.
我们推导了一族涉及量子态不同相空间分布的不等式，任何经典态都必须满足这些不等式。违背这些不等式是量子非经典性的明确标志。我们的方法将通过相空间分布中的负值来表征非经典效应与通常为物理可观测量的矩所制定的不等式条件相结合。重要的是，即使所涉及的相空间分布是非负的，所得到的判据也能证明量子非经典性。此外，我们展示了这些不等式与关联测量是如何相关的。通过不同的例子，包括压缩态、有损单光子态甚至相干态，证明了所推导条件的强度。
