Detecting a phonon flux in superfluid He4 by a nanomechanical resonator

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 He can be excited by a modulated flux of phonons. A nanosized heater immersed in superfluid 4 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.

Fundamental dissipation due to bound fermions in the zero-temperature limit

“…On the other hand, it seems essential to enhance the experiment presented in this article by building a detector or spectrometer fast enough to distinguish the dissipation associated with the separate phases of the wire motion. This requires designing and devising nano-sized instruments 1,2 .…”

“…Phenomenologically, the hysteretic contribution follows ΔQ ¼ aðv=v c Þ 1=2 (Fig. 4a, b), where a ∝ (ΔI) 2 (Fig. 4c).…”

“…Interfaces in fermionic condensates and the bound states hosted by them have recently attracted research focus in numerous condensed matter systems. Contemporary superfluid research is moving towards nanoscale probes 1 , 2 , nanoconfinement 3 – 5 and microscopic dissipation mechanisms related to quantum turbulence 6 , 7 . Unconventional superconductivity in various materials 8 and the dynamics of certain atomic BECs 9 is characterised by the physics of bound excitations.…”

“…The fitted values of a are shown in panel (c): Fits to data where Δt = 0 are shown with black circles, Δt = 50 ms corresponds to blue squares, and Δt = 100 ms is shown as red triangles. The dashed line is a guide to the eye that corresponds to a = −5.0/H 2 nJ mT2 . Panel (d) shows fitted values of b (black circles), which within the scatter of the data are independent of H as expected.…”

Nanoscale Real-Time Detection of Quantum Vortices at Millikelvin Temperatures

“…The nanobeams we use for detecting single vortex events in real time have a characteristic dimension less than 1 µm and response times faster than 1 ms. Such devices have recently emerged as highly sensitive probes of hydrodynamic 2,3 and ballistic 4 He 4,5 . We present here events demonstrating single-vortex capture, its interaction with the surrounding vortex tangle, and subsequent release via reconnection with a nearby vortex in the surrounding tangle.…”