A first demonstration of active feedback control and multi-frequency imaging techniques for kinetic inductance detectors

TL;DR

This paper demonstrates a novel active feedback control and multi-frequency imaging method for superconducting resonators, enabling improved resonance tracking and response analysis in kinetic inductance detectors.

Contribution

It introduces a multi-frequency imaging technique and a proof-of-concept feedback algorithm for resonance control in superconducting resonators.

Findings

Multi-frequency imaging reveals resonator responses not seen in traditional scans.

Feedback control maintains resonator frequency despite loading variations.

The approach improves linearity and reduces crosstalk in kinetic inductance detectors.

Abstract

RF-ICE is a signal processing platform for the readout of large arrays of superconducting resonators. Designed for flexibility, the system's low digital latency and ability to independently and dynamically set the frequency and amplitude of probe tones in real time has enabled previously-inaccessible views of resonator behaviour, and opened the door to novel resonator control schemes. We introduce a multi-frequency imaging technique, developed with RF-ICE, which allows simultaneous observation of the entire resonance bandwidth. We demonstrate the use of this technique in the examination of the response of superconducting resonators to variations in applied readout current and thermal loading. We observe that, used in conjunction with a conventional frequency sweep at sufficiently large amplitude to induce resonance bifurcation, the multi-frequency imaging technique reveals a resonator response which is not captured by the frequency sweep measurement alone. We demonstrate that equivalent resonant frequency shifts can be achieved using either thermal, optical, or readout loading, and use this equivalence to counteract a change in thermal loading by digitally modulating the readout current through a resonator. We develop and implement a proof-of-concept closed-loop negative electro-quasiparticle feedback algorithm which first sets and then maintains the resonant frequency of a lumped element kinetic inductance detector while the loading on it is varied. Although this simple implementation is not yet suitable to deploy at scale, it demonstrates the utility of this feedback technique to improve linearity while addressing amplifier distortion, resonator response non-uniformity, and crosstalk. It can be applied to kinetic inductors in non-bolometric operation, and sets the stage for future developments.