A First Demonstration of the SQUAT Detector Architecture: Direct Measurement of Resonator-Free Charge-Sensitive Transmons
H. Magoon, T. Aralis, T. Dyson, J. Anczarski, D. Baxter, G. Bratrud, R. Carpenter, S. Condon, A. Droster, E. Figueroa-Feliciano, C. W. Fink, S. Harvey, A. Simchony, Z. J. Smith, S. Stevens, N. Tabassum, B. A. Young, C. P. Salemi, K. Stifter, D. I. Schuster, N. A. Kurinsky
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.