Electromechanical feedback control of nanoscale superflow

TL;DR

This paper demonstrates electromechanical control of superfluid helium-4 within a nanofluidic resonator, enabling measurement, feedback-induced self-oscillation, damping, and frequency tuning of superflow modes, advancing superfluid optomechanics.

Contribution

It introduces a novel electromechanical coupling to superfluid helium-4 in a nanofluidic resonator, enabling active control and measurement of superflow modes.

Findings

Successful measurement of displacement and velocity of superfluid modes.

Implementation of feedback for self-oscillation and damping.

Tuning of superflow mode frequency through feedback control.

Abstract

Superfluid $^4$He is a promising material for optomechanical and electromechanical applications due to its low acoustic loss. Some of the more intriguing aspects of superfluidity -- the macroscopic coherence, topological nature of vorticity, and capability of supporting non-classical flows -- remain, however, poorly explored resources in opto- and electro-mechanical systems. Here, we present an electromechanical coupling to pure superflow inside a nanofluidic Helmholtz resonator with viscously clamped normal fluid. The system is capable of simultaneous measurement of displacement and velocity of the Helmholtz mechanical mode weakly driven by incoherent environmental noise. Additionally, we implement feedback capable of inducing self-oscillation of the non-classical acoustic mode, damping the motion below the ambient level, and tuning of the mode frequency.