Superfluid Brillouin Optomechanics

TL;DR

This paper presents a novel optomechanical system using superfluid helium as the mechanical resonator, demonstrating strong coupling and thermal motion detection with low phonon numbers in a cryogenic environment.

Contribution

It introduces a superfluid helium-based optomechanical system with high coupling rates and unique mechanical properties, expanding the range of accessible phenomena.

Findings

Achieved an optomechanical coupling rate of ~3 kHz.

Successfully observed superfluid thermal motion with a mean phonon number as low as 11.

Demonstrated the system's potential for low-loss, cryogenic optomechanics.

Abstract

Optomechanical systems couple an electromagnetic cavity to a mechanical resonator which is typically formed from a solid object. The range of phenomena accessible to these systems depends on the properties of the mechanical resonator and on the manner in which it couples to the cavity fields. In both respects, a mechanical resonator formed from superfluid liquid helium offers several appealing features: low electromagnetic absorption, high thermal conductivity, vanishing viscosity, well-understood mechanical loss, and in situ alignment with cryogenic cavities. In addition, it offers degrees of freedom that differ qualitatively from those of a solid. Here, we describe an optomechanical system consisting of a miniature optical cavity filled with superfluid helium. The cavity mirrors define optical and mechanical modes with near-perfect overlap, resulting in an optomechanical coupling rate ~3 kHz. This coupling is used to drive the superfluid; it is also used to observe the superfluid's thermal motion, resolving a mean phonon number as low as 11.