M. B. Rothwell

Environmental Radiation Impact on Lifetimes and Quasiparticle Tunneling Rates of Fixed-Frequency Transmon Qubits

  1. R.T. Gordon,
  2. C. E. Murray,
  3. C. Kurter,
  4. M. Sandberg,
  5. S.A. Hall,
  6. K. Balakrishnan,
  7. R. Shelby,
  8. B. Wacaser,
  9. A.A. Stabile,
  10. J.W. Sleight,
  11. M. Brink,
  12. M. B. Rothwell,
  13. K. Rodbell,
  14. O. Dial,
  15. and M. Steffen
Quantum computing relies on the operation of qubits in an environment as free of noise as possible. This work reports on measuring the impact of environmental radiation on lifetimes
of fixed frequency transmon qubits with various capacitor pad geometries by varying the amount of shielding used in the measurement space. It was found that the qubit lifetimes are robust against these shielding changes until the most extreme limit was tested without a mixing chamber shield in the refrigerator. In contrast, the quasiparticle tunneling rates were found to be extremely sensitive to all configurations tested, indicating these devices are not yet limited by losses related to superconducting quasiparticles.
arxiv pdf

Improved superconducting qubit coherence using titanium nitride

  1. J. Chang,
  2. M. R. Vissers,
  3. A. D. Corcoles,
  4. M. Sandberg,
  5. J. Gao,
  6. David W. Abraham,
  7. Jerry M. Chow,
  8. Jay M. Gambetta,
  9. M. B. Rothwell,
  10. G. A. Keefe,
  11. Matthias Steffen,
  12. and D. P. Pappas
We demonstrate enhanced relaxation and dephasing times of transmon qubits, up to ~ 60 mu s by fabricating the interdigitated shunting capacitors using titanium nitride (TiN). Compared
to lift-off aluminum deposited simultaneously with the Josephson junction, this represents as much as a six-fold improvement and provides evidence that previous planar transmon coherence times are limited by surface losses from two-level system (TLS) defects residing at or near interfaces. Concurrently, we observe an anomalous temperature dependent frequency shift of TiN resonators which is inconsistent with the predicted TLS model.
arxiv pdf