A Quasiparticle Detector for Imaging Quantum Turbulence in Superfluid $$^3$$ 3 He-B

Abstract

We describe the development of a two-dimensional quasiparticle detector for use in visualising quantum turbulence in superfluid 3 He-B at ultra-low temperatures. The detector consists of a 5 × 5 matrix of pixels, each a 1 mm diameter hole in a copper block containing a miniature quartz tuning fork. The damping on each fork provides a measure of the local quasiparticle flux. The detector is illuminated by a beam of ballistic quasiparticles generated from a nearby black-body radiator. A comparison of the damping on the different forks provides a measure of the cross-sectional profile of the beam. Further, we generate a tangle of vortices (quantum turbulence) in the path of the beam using a vibrating wire resonator. The vortices cast a shadow onto the face of the detector due to the Andreev reflection of quasiparticles in the beam. This allows us to image the vortices and to investigate their dynamics. Here we give details of the design and construction of the detector and show some preliminary results for one row of pixels which demonstrates its successful application to measuring quasiparticle beams and quantum turbulence.

ANDREEV REFLECTION IN ROTATING SUPERFLUID3He-B

“…Further improvement is expected, if arrays of quartz tuning forks [6] or of resonators fabricated as micro-electromechanical systems (MEMS) become available as quasiparticle detectors. During the past decade it has been demonstrated that the zero temperature limit of 3 He-B can also be reached and explored in rotation.…”

“…More recently the ultra-low temperature regime of 3 He-B has moved in the forefront of general interest when it was realized that conventional sub-mK refrigeration techniques by means of adiabatic demagnetization cooling of copper are quite adequate if the total heat leak to the sample volume can be reduced to below ∼ 20 pW. This recognition has led to the development of new measuring techniques for the ballistic regime in superfluid 3 He which are based on the use of mechanical vibrating resonance devices [6] or the existence of a novel coherently precessing NMR mode [7]. Such work has been driven by the hope to reveal explicit new information on Andreev reflection, or on the existence of Andreev bound states on surfaces, interfaces, and vortex cores, or the expectation to identify the Majorana character in the spectrum of the bound state excitations [8].…”

Development of a Spatially Resolved $$^3$$He Quasi-Particle Detector

“…With such a detector, we hope to make measurements similar to angleresolved photo-emission spectroscopy. For example, there are several potential sources of quasi-particles that produce a well-defined beam profile, such as black-body radiators [10,11]. The source could be used to illuminate a surface of the fluid with quasi-particles, while using the detector to measure the reflected flux.…”

“…The deviations in flux from that expected from a surface without bound states will tell us about the momentum transfer between bulk and surface states. The detector can also be used as a quasi-particle camera to image flow structures in 3 He, such as quantum turbulence [11].…”

Quartz tuning fork as a probe of surface oscillations

“…Tuning forks are nowadays widely exploited in helium low temperature experiments as thermometers, viscometers, pressure sensors, turbulence detectors, etc. 13,14 In our measurement scheme resembling the so-called near-field acoustic microscopy, 15,16 an oscillating quartz tuning fork is placed in the vicinity of the surface of the solid. A change in the distance z between the interface and the fork distorts the velocity field in the liquid around the oscillating fork and thus changes its effective hydrodynamic mass.…”