G. Bratrud

TLS loss in superconducting resonators on epitaxial hBN thin films

  1. J. Christiansen-Salameh,
  2. D.J. Temples,
  3. R. Linehan,
  4. S. Sussman,
  5. Aloyse Maille,
  6. F. Abouzahr,
  7. L. Alexis,
  8. K. Anyang,
  9. D. Bowring,
  10. G. Bratrud,
  11. E. Celi,
  12. A.H. Colón Cesaní,
  13. R. Khatiwada,
  14. D. Molenaar,
  15. O. Peek,
  16. A. Rodriguez,
  17. O. Seidel,
  18. D. Schlom,
  19. D. Sotir,
  20. S. Uemura,
  21. Y. Wu,
  22. E. Figueroa-Feliciano,
  23. D. Baxter,
  24. and Z. Tian
The integration of low-loss dielectrics into superconducting circuits is of importance to the functionality of quantum computers and sensors. In this work, we fabricate and measure
niobium resonators atop few-layer, epitaxial hexagonal boron nitride (hBN) grown by Molecular Beam Epitaxy on a sapphire substrate and compare against a control counterpart without hBN. We conduct radiofrequency measurements which probe the responses to power, temperature, and temporal fluctuations of two-level systems. The resonators integrating hBN maintain low dielectric loss with a low-power internal loss tangent on the order of 10−6, and demonstrate hBN can be added to the conventional superconducting qubit stack with minimal degradation of the quality factor. This research represents a first step towards a materials-driven strategy to eliminate phonon-mediated correlated errors in solid-state quantum systems, which leverages the thermal properties of 2D materials to prevent athermal phonons excited in the device substrate from transmitting across the superconductor-substrate interface. The same technique applied to quantum sensors would maximize phonon collection by blocking phonons from entering passive metal films.
arxiv pdf

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.
arxiv pdf