Contact-less phonon detection with massive cryogenic absorbers

Abstract

We have developed a contactless technique for the real time measurement of athermal (Cooper-pair breaking) phonons in an absorber held at subkelvin temperatures. In particular, a thin-film aluminum superconducting resonator was realized on a 30 g high-resistivity silicon crystal. The lumped-element resonator is inductively excited/readout by a radio frequency microstrip feed-line deposited on another wafer; the sensor, a kinetic inductance detector, is readout without any physical contact or wiring to the absorber. The resonator demonstrates excellent electrical properties, particularly in terms of its internal quality factor. The detection of alphas and gammas in the massive absorber is achieved, with an RMS energy resolution of about 1.4 keV, which is already interesting for particle physics applications. The resolution of this prototype detector is mainly limited by the low (≈ 0.3 %) conversion efficiency of deposited energy to superconducting excitations (quasiparticles). The demonstrated technique can be further optimized and used to produce large arrays of athermal phonon detectors, for use in rare event searches such as dark matter direct detection, neutrinoless double beta decay, or coherent elastic neutrino-nucleus scattering.