Thermal intermodulation backaction in a high-cooperativity optomechanical system

TL;DR

This paper demonstrates thermal intermodulation noise backaction in a high-cooperativity room temperature optomechanical system, revealing a significant source of optical noise that could hinder quantum regime achievement.

Contribution

It reports the first observation of TIN backaction in a high-cooperativity, room temperature optomechanical system, highlighting its impact on quantum optomechanics.

Findings

TIN backaction exceeds thermal noise by 20 dB

TIN backaction exceeds shot noise by 40 dB

Thermal motion is 10 times smaller than cavity linewidth

Abstract

The pursuit of room temperature quantum optomechanics with tethered nanomechanical resonators faces stringent challenges owing to extraneous mechanical degrees of freedom. An important example is thermal intermodulation noise (TIN), a form of excess optical noise produced by mixing of thermal noise peaks. While TIN can be decoupled from the phase of the optical field, it remains indirectly coupled via radiation pressure, implying a hidden source of backaction that might overwhelm shot noise. Here we report observation of TIN backaction in a high-cooperativity, room temperature cavity optomechanical system consisting of an acoustic-frequency Si$_3$N$_4$ trampoline coupled to a Fabry-P\'{e}rot cavity. The backaction we observe exceeds thermal noise by 20 dB and radiation pressure shot noise by 40 dB, despite the thermal motion being 10 times smaller than the cavity linewidth. Our results suggest that mitigating TIN may be critical to reaching the quantum regime from room temperature in a variety of contemporary optomechanical systems.