Mutual emergence of noncausal optical response and nonclassicality in an optomechanical system

TL;DR

This paper demonstrates that nonclassical light and noncausal optical responses in an optomechanical cavity appear simultaneously at a critical coupling, linking quantum and classical phenomena through boundary conditions and wave relations.

Contribution

It reveals the simultaneous emergence of nonclassicality and noncausality in optomechanical systems at a specific coupling, independent of cavity boundary conditions.

Findings

Nonclassicality and noncausality emerge at the same critical coupling.

The emergence is independent of cavity length and boundary conditions.

Relations with entanglement and superfluid vacuum are discussed.

Abstract

We show that single-mode nonclassicality of the output of an optomechanical cavity and the noncausal linear optical response of this cavity emerge at the same critical cavity-mechanical coupling. In other words, single-mode nonclassicality emerges when the barrier (in electromagnetism) avoiding faster-than-light communication is lifted off. The nature of the emergence of noncausal behavior does not depend on the length (boundary conditions) and the type of the cavity. Origin of the noncausal behavior is the temporal/frequency relations between the incident and reflected waves at the outer surface of the cavity. We further discuss the relations with the recent studies; (i) equivalence of the entanglement among identical particles to the nonclassicality of their quasiparticle excitations, (ii) necessity of superfluid behavior of vacuum, and (iii) entanglement-wormhole equivalence.