A First Demonstration of the SQUAT Detector Architecture: Direct Measurement of Resonator-Free Charge-Sensitive Transmons

TL;DR

This paper introduces the SQUAT detector architecture for THz detection, demonstrating its ability to directly measure charge and quasiparticle signals in superconducting transmons, marking a significant step in quantum sensing technology.

Contribution

The paper presents the first design and experimental validation of the SQUAT architecture, a novel superconducting sensor for direct charge and quasiparticle detection.

Findings

Successful demonstration of simultaneous charge and quasiparticle detection.

Initial characterization of prototype SQUAT devices.

Identification of background sources affecting parity-switching rate.

Abstract

The Superconducting Quasiparticle-Amplifying Transmon (SQUAT) is a new sensor architecture for THz (meV) detection based on a weakly charge-sensitive transmon directly coupled to a transmission line. In such devices, energy depositions break Cooper pairs in the qubit capacitor islands, generating quasiparticles. Quasiparticles that tunnel across the Josephson junction change the transmon qubit parity, generating a measurable signal. In this paper, we present the design of first-generation SQUATs and demonstrate an architecture validation. We summarize initial characterization measurements made with prototype devices, comment on background sources that influence the observed parity-switching rate, and present experimental results showing simultaneous detection of charge and quasiparticle signals using aluminum-based SQUATs.