Cavity Optomechanics in a Levitated Helium Drop

TL;DR

This paper proposes a novel optomechanical system using a magnetically levitated liquid helium drop in vacuum, combining optical, mechanical, and cooling functionalities, enabling studies of superfluid motion and quantum measurements.

Contribution

It introduces a new levitated helium drop system integrating optical whispering gallery modes, surface vibrations, and evaporative cooling, with potential for strong photon-phonon coupling and quantum experiments.

Findings

Feasibility of magnetic levitation of helium drops demonstrated

High optical quality factors achievable at low temperatures

Potential to study superfluid dynamics and quantum non-demolition measurements

Abstract

We describe a proposal for a new type of optomechanical system based on a drop of liquid helium that is magnetically levitated in vacuum. In the proposed device, the drop would serve three roles: its optical whispering gallery modes would provide the optical cavity, its surface vibrations would constitute the mechanical element, and evaporation of He atoms from its surface would provide continuous refrigeration. We analyze the feasibility of such a system in light of previous experimental demonstrations of its essential components: magnetic levitation of mm-scale and cm-scale drops of liquid He, evaporative cooling of He droplets in vacuum, and coupling to high-quality optical whispering gallery modes in a wide range of liquids. We find that the combination of these features could result in a device that approaches the single-photon strong coupling regime, due to the high optical quality factors attainable at low temperatures. Moreover, the system offers a unique opportunity to use optical techniques to study the motion of a superfluid that is freely levitating in vacuum (in the case of $^{4}\mathrm {He}$). Alternatively, for a normal fluid drop of $^3 \mathrm{He}$, we propose to exploit the coupling between the drop's rotations and vibrations to perform quantum non-demolition measurements of angular momentum.