Magnetic field tunable spectral response of kinetic inductance detectors

TL;DR

This paper demonstrates how applying an external magnetic field can tune the spectral response of aluminium kinetic inductance detectors by decreasing their superconducting gap, enabling potential spectroscopic applications.

Contribution

It introduces a method to tune the spectral response of kinetic inductance detectors using magnetic fields, highlighting the effects on superconducting gap and quality factor.

Findings

Spectral response shifted from 90 GHz to 60 GHz with magnetic field

Superconducting gap decreased from 90 GHz to 60 GHz at 3 mT

Internal quality factor exhibits hysteresis due to vortices

Abstract

We tune the onset of optical response in aluminium kinetic inductance detectors from a natural cutoff frequency of 90 GHz to 60 GHz by applying an external magnetic field. The change in spectral response is due to the decrease of the superconducting gap, from 90 GHz at zero magnetic field to 60 GHz at a magnetic field of around 3 mT. We characterize the variation of the superconducting gap, the detector frequency shift and the internal quality factor as a function of the applied field. In principle, the magnetic field tunable response could be used to make spectroscopic measurements. In practice, the internal quality factor behaves hysteretically with the magnetic field due to the presence of vortices in the thin superconducting film. We conclude by discussing possible solutions to achieve spectroscopy measurements using kinetic inductance detectors and magnetic field.