# Contact-less phonon detection with massive cryogenic absorbers

## TL;DR

This paper introduces a contact-less, superconducting resonator-based phonon detector on a massive silicon absorber, achieving keV energy resolution suitable for rare event physics, with potential for large-scale applications.

## Contribution

It presents a novel contact-less phonon detection method using a superconducting resonator on a large absorber, enabling real-time, high-resolution measurements without physical wiring.

## Key findings

- Achieved RMS energy resolution of ~1.4 keV.
- Demonstrated detection of alpha and gamma events.
- Resonator shows excellent internal quality factor.

## Abstract

We have developed a contact-less technique for the real time measurement of a-thermal (Cooper-pair breaking) phonons in an absorber held at sub-Kelvin temperatures. In particular, a thin-film aluminum superconducting resonator was realized on a 30-grams high-resistivity silicon crystal. The lumped-element resonator is inductively excited/read-out by a radio-frequency microstrip feed-line deposited on another wafer; the sensor, a Kinetic Inductance Detector (KID), is read-out 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 (about 0.3%) conversion efficiency of deposited energy to superconducting excitations (quasi-particles). The demonstrated technique can be further optimized, and used to produce large arrays of a-thermal phonon detectors, for use in rare events searches such as: dark matter direct detection,neutrino-less double beta decay, or coherent elastic neutrino-nucleus scattering.