Stationary optomechanical entanglement between a mechanical oscillator and its measurement apparatus

TL;DR

This paper demonstrates that stationary entanglement between a mechanical oscillator and light can be inferred through continuous measurement of the light field, even in non-sideband-resolved regimes, with potential applications in quantum sensing.

Contribution

It introduces an experimentally feasible scheme to detect optomechanical entanglement via light squeezing measurements in a standard sensor configuration.

Findings

Entanglement can be inferred from squeezing in the output light.

Squeezing levels up to 50% noise reduction are achievable.

Entanglement persists even at low quantum cooperativity.

Abstract

We provide an argument to infer stationary entanglement between light and a mechanical oscillator based on continuous measurement of light only. We propose an experimentally realizable scheme involving an optomechanical cavity driven by a resonant, continuous-wave field operating in the non-sideband-resolved regime. This corresponds to the conventional configuration of an optomechanical position or force sensor. We show analytically that entanglement between the mechanical oscillator and the output field of the optomechanical cavity can be inferred from the measurement of squeezing in (generalized) Einstein-Podolski-Rosen quadratures of suitable temporal modes of the stationary light field. Squeezing can reach levels of up to 50% of noise reduction below shot noise in the limit of large quantum cooperativity. Remarkably, entanglement persists even in the opposite limit of small cooperativity. Viewing the optomechanical device as a position sensor, entanglement between mechanics and light is an instance of object-apparatus entanglement predicted by quantum measurement theory.