# Detecting the "phonon wind" in superfluid $\mathrm{^4He}$ by a nanomechanical resonator

## TL;DR

This paper demonstrates that nanoscale mechanical resonators immersed in superfluid helium-4 can be excited by a modulated phonon flux, revealing a ballistic phonon wind effect that could enable novel quantum fluid experiments.

## Contribution

It introduces a method to detect phonon wind in superfluid helium-4 using nanomechanical resonators, a novel approach in quantum fluid research.

## Key findings

- Resonators can be excited by modulated phonon flux in superfluid helium-4.
- Ballistic phonon wind can be detected via resonator motion.
- Potential for new quantum fluid experiments using this effect.

## Abstract

Nanoscale mechanical resonators are widely utilized to provide high sensitivity force detectors. Here we demonstrate that such high quality factor resonators immersed in superfluid \(^4\mathrm{He}\) can be excited by a modulated flux of phonons. A nanosized heater immersed in superfluid \(^4\mathrm{He}\) acts as a source of ballistic phonons in the liquid -- "phonon wind". When the modulation frequency of the phonon flux matches the resonance frequency of the mechanical resonator, the motion of the latter can be excited. This ballistic thermomechanical effect can potentially open up new types of experiments in quantum fluids.