Nonclassicality of noisy quantum states

Nonclassicality conditions for an oscillator-like system interacting with a hot thermal bath are considered. Nonclassical properties of quantum states can be conserved up to a certain temperature threshold only. In this case, affection of the thermal noise can be compensated via transformation of an observable, which tests the nonclassicality (witness function). Possibilities for experimental implementations based on unbalanced homodyning are discussed. At the same time, we demonstrate that the scheme based on balanced homodyning cannot be improved for noisy states with proposed technique and should be applied directly.Comment: 15 pages, 3 figure

Dual problem of nonclassicality

We show that nonclassicality of phase-space quasi-probability distributions is tied to violations of principles of physical reality in device-dependent scenarios. In this context, the nonclassicality problem has its dual form expressed as a device-dependent analog of Bell inequalities. This approach is applicable even to systems with only one spatial party. The derived inequalities are employed for testing nonclassicality with emblematic optical measurements: photocounting including the case of realistic photon-number resolution; unbalanced, balanced, and eight-port homodyne detection.Comment: 13 pages, 6 figure