Tunable sub-gap radiation detection with superconducting resonators

TL;DR

This paper introduces tunable superconducting resonators made from amorphous Indium Oxide that detect sub-gap radiation by frequency shifts, with the detection frequency adjustable via resonator length modulation, offering a new approach to radiation detection.

Contribution

The study demonstrates a novel type of superconducting detector, SKIDs, which operate below the superconducting gap and allow frequency tuning through resonator length adjustments, differing from traditional KIDs.

Findings

Resonators detect 7-10 GHz radiation via frequency shifts.

Detection frequency is tunable by changing resonator length.

Coupling arises from kinetic inductance non-linearity.

Abstract

We have fabricated planar amorphous Indium Oxide superconducting resonators ($T_c\sim2.8$ K) that are sensitive to frequency-selective radiation in the range of 7 to 10 GHz. Those values lay far below twice the superconducting gap that worths about 200 GHz. The photons detection consists in a shift of the fundamental resonance frequency. We show that the detected frequency can be adjusted by modulating the total length of the superconducting resonator. We attribute those observations to the excitation of higher-order resonance modes. The coupling between the fundamental lumped and the higher order distributed resonance is due to the kinetic inductance non-linearity with current. These devices, that we have called Sub-gap Kinetic Inductance Detectors (SKIDs), are to be distinguished from the standard Kinetic Inductance Detectors (KIDs) in which quasi-particles are generated when incident light breaks down Cooper pairs.