A New Tool for Sensing Phonons in Liquid Helium

To probe the physical properties of quantum fluids, some researchers are turning to vibrating microscopic threads of material known as nanomechanical resonators. By dunking the resonators in the fluid and observing how the fluid damps the resonators’ oscillations, physicists hope to go fishing for quasiparticles or explore questions surrounding quantum turbulence and superfluidity. Now, Andrew Guthrie of Lancaster University in the UK and colleagues have taken nanoresonators where they’ve never gone before: liquid helium-4 cooled to a few thousandths of a degree above absolute zero. The resonators snagged collective oscillations in the fluid known as phonons in experiments that showcase the probe’s sensitivity.