Membrane-in-the-middle optomechanics with a soft-clamped membrane at milliKelvin temperatures

TL;DR

This paper demonstrates a vibration-isolated optical cavity with a soft-clamped silicon nitride membrane at milliKelvin temperatures, achieving dynamical backaction and analyzing heating effects on coherence time.

Contribution

It introduces an actuator-free cavity design mounted on a vibration-isolation platform, enabling strong optomechanical coupling at cryogenic temperatures.

Findings

Dynamical backaction observed near the red sideband.

Coherence time scales inversely with intracavity power.

Vibration isolation effectively reduces noise in the system.

Abstract

Soft-clamped silicon nitride membrane resonators reach coherence times tau in excess of 100 ms at milliKelvin bath temperatures. However, harnessing strong optomechanical coupling in dry dilution refrigerators remains challenging due to vibration issues and heating by optical absorption. Here, we propose to address these issues with an actuator-free optical cavity and mechanical resonator design, in which the cavity is mounted on a simple vibration-isolation platform. We observe dynamical backaction when the cavity is driven with a free-space optical beam stabilized close to the red sideband using a two-beam locking scheme. Finally, we characterize the effect of absorption heating on the coherence time, and find a scaling with the intracavity power P as tau proportional to P to the power of -(0.34+/-0.04).