Multimode optomechanical system in the quantum regime

TL;DR

This paper demonstrates a robust multimode optomechanical system operating in the quantum regime, achieving quantum measurement backaction and observing ponderomotive squeezing with multiple long-lived mechanical modes at cryogenic temperatures.

Contribution

It introduces a simple, stable system with high-Q mechanical modes and demonstrates quantum measurement backaction and ponderomotive squeezing in a multimode optomechanical setup.

Findings

Quantum measurement rate exceeds mechanical decoherence rates at 10 K.

Observed ponderomotive squeezing up to -2.4 dB.

System supports hybrid entanglement schemes with multiple degrees of freedom.

Abstract

We realise a simple and robust optomechanical system with a multitude of long-lived ($Q>10^7$) mechanical modes in a phononic-bandgap shielded membrane resonator. An optical mode of a compact Fabry-Perot resonator detects these modes' motion with a measurement rate ($96~\mathrm{kHz}$) that exceeds the mechanical decoherence rates already at moderate cryogenic temperatures ($10\,\mathrm{K}$). Reaching this quantum regime entails, i.~a., quantum measurement backaction exceeding thermal forces, and thus detectable optomechanical quantum correlations. In particular, we observe ponderomotive squeezing of the output light mediated by a multitude of mechanical resonator modes, with quantum noise suppression up to -2.4 dB (-3.6 dB if corrected for detection losses) and bandwidths $\lesssim 90\,\mathrm{ kHz}$. The multi-mode nature of the employed membrane and Fabry-Perot resonators lends itself to hybrid entanglement schemes involving multiple electromagnetic, mechanical, and spin degrees of freedom.