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

  1. H. Magoon,
  2. T. Aralis,
  3. T. Dyson,
  4. J. Anczarski,
  5. D. Baxter,
  6. G. Bratrud,
  7. R. Carpenter,
  8. S. Condon,
  9. A. Droster,
  10. E. Figueroa-Feliciano,
  11. C.W. Fink,
  12. S. Harvey,
  13. A. Simchony,
  14. Z.J. Smith,
  15. S. Stevens,
  16. N. Tabassum,
  17. B.A. Young,
  18. C.P. Salemi,
  19. K. Stifter,
  20. D.I. Schuster,
  21. and N. A. Kurinsky
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.
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