# Backaction-evading measurement of entanglement in optomechanics

## TL;DR

This paper introduces a fully backaction-evading measurement scheme for directly detecting entanglement between two nanomechanical resonators using a specialized cavity drive and detection tone configuration.

## Contribution

It presents a novel measurement protocol that enables direct, backaction-free observation of entanglement in optomechanical systems.

## Key findings

- Demonstrates a method for entanglement detection without backaction disturbance
- Shows how to reconstruct collective quadrature fluctuations of mechanical resonators
- Provides a way to verify entanglement properties directly

## Abstract

We propose here a fully backaction-evading scheme for the measurement of the entanglement between two nanomechanical resonators. The system, which consists of two mechanical oscillators, coupled to a single mode of an electromagnetic resonant cavity through a radiation-pressure interaction term, is driven by two pump tones and four detection tones. As previously discussed in the literature, the former induce entanglement between the two mechanical oscillators, while we show here that a specific choice of phase and amplitude of the detection tones allows for direct pairwise reconstruction of the collective quadrature fluctuations of the mechanical oscillators belonging to quantum-mechanics-free subspaces, thereby providing direct evidence of the entanglement properties of the two mechanical resonators.