Witnessing nonclassicality of a quantum oscillator state by coupling it to a qubit

Abstract

We propose a new witness operation for the non-classical character of a harmonic oscillator state. The method does not require state reconstruction. For all harmonic oscillator states that are classical, a bound is established for the evolution of a qubit which is coupled to the oscillator. Any violation of the bound can be rigorously attributed to the non-classical character of the initial oscillator state.

Pulsed characteristic-function measurement of a thermalizing harmonic oscillator

“…i.e., a probe-state dependent constant force acting on the harmonic oscillator [14,33], with the same strength but opposite signs depending on the probe state. Such a coupling can be realized in a variety of electromechanical systems, for example, when an electronic spin is coupled to the motional degree of freedom of a mechanical element emanating a magnetic field or is embedded in a mechanical oscillator subject to a spatially inhomogeneous magnetic field [34][35][36].…”

Effect of relativistic motion on witnessing nonclassicality of quantum states

“…Observed violation of the witness inequality indicates that the P -representation of the initial state ρ ho (0) has been negative, thus non-classical. However, a lack of this violation does not guarantee that ρ ho (0) can be considered classical, as shown in particular examples in [33]. For a better understanding of the witness function let us look at quantum states that reveal their nonclassicality when tested within this formalism.…”

“…The upper bound dictated by the classicality of the P -representation is violated periodically. Moreover, this violation, if present, occurs only after a certain minimum time and for λ above a certain threshold value [33].…”

Gaussian state entanglement witnessing through lossy compression

“…In this work we focus on the problem how to extract information about entanglement in the state of a complex bipartite system A. The main idea is to pair A with a simple system B [10]. A is assumed to be difficult to analyze, whereas B allows full analysis.…”