More nonlocality with less entanglement in a tripartite atom‐optomechanical system

Abstract

We study quantum effects in hybrid atomic optomechanics in a system comprising a cloud of atoms and a mobile mirror mediated by a single-mode cavity. Tripartite nonlocality is observed in the atom-light-mirror system, as demonstrated by the violation of the Mermin-Klyshko (MK) inequality. It has been shown [C. Genes, et al., PRA 77, 050307 (R) (2008)] that tripartite entanglement is optimized when the cavity is resonant with the anti-Stokes sideband of the driving laser and the atomic frequency matches the Stokes one. However, we show that this is not the case for the nonlocality. The MK function achieves minima when the atoms are resonant with both the Stokes and anti-Stokes sidebands, and unexpectedly, we find violation of the MK inequality only in a parameter region where entanglement is far from being maximum. A negative relation exists between nonlocality and entanglement with consideration of the possibility of bipartite nonlocality in the violation of the MK inequality. We also study the non-classicality of the mirror by post-selected measurements, e.g. Geiger-like detection, on the cavity and/or the atoms. We show that with feasible parameters Geiger-like detection on the atoms can effectively induce mechanical non-classicality. PACS numbers:The lack of observation of quantum effects at the macroscopic scale reinforces the conjecture that macroscopic objects are governed by classical physics, while the microscopic world is ruled by quantum mechanics. However, quantum mechanics intrinsically shows no limitation to describe largescale/massive systems [1]. Preparing macroscopic quantum states is of vital importance for understanding fundamental issues in quantum mechanics, such as decoherence and the quantum-to-classical transition [2], collapse models of the wave function [3], and so on. Optomechanics, addressing the coupling of optical and mechanical degrees of freedom via radiation pressure [4], provides an ideal platform to generate and control quantum mesoscopic/macroscopic states of mechanical systems thanks to its intrinsic nonlinear light-matter interactions.Over the past few years, successful advances in nano-and micro-mechanical engineering, in particular mechanical oscillators cooled into (or close to) their ground state [5,6], have made it possible to prepare mechanical quantum states. Preparing quantum states either for the light mode or the mechanical oscillator is a fascinating (though challenging) goal in the field of optomechanics [7,8]. Nonclassical mechanical states can be generated by the optomechanical nonlinearity intrinsic in the strong coupling regime [9,10], by injecting squeezed light into the cavity (the squeezing is thus transferred from light to the mechanical degree of freedom) [11,12], by post-selected measurements on the optical field [13,14], and so on.Recently, it has been reported that hybrid atom-assisted optomechanics shows advantages in many aspects [15]. To name but a few, atoms induce an additional nonlinear effect, which enhances the optomechanical interaction and...

Perfect controlled joint remote state preparation independent of entanglement degree of the quantum channel

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Perfect Transfer of enhanced entanglement and asymmetric steering in a cavity magnomechanical system

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Nonclassical-state generation in macroscopic systems via hybrid discrete-continuous quantum measurements

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