C. D. Wilen

Correlated Charge Noise and Relaxation Errors in Superconducting Qubits

  1. C. D. Wilen,
  2. S. Abdullah,
  3. N. A. Kurinsky,
  4. C. Stanford,
  5. L. Cardani,
  6. G. D'Imperio,
  7. C. Tomei,
  8. L. Faoro,
  9. L.B. Ioffe,
  10. C. H. Liu,
  11. A. Opremcak,
  12. B. G. Christensen,
  13. J. L. DuBois,
  14. and R. McDermott
The central challenge in building a quantum computer is error correction. Unlike classical bits, which are susceptible to only one type of error, quantum bits („qubits“)
are susceptible to two types of error, corresponding to flips of the qubit state about the X- and Z-directions. While the Heisenberg Uncertainty Principle precludes simultaneous monitoring of X- and Z-flips on a single qubit, it is possible to encode quantum information in large arrays of entangled qubits that enable accurate monitoring of all errors in the system, provided the error rate is low. Another crucial requirement is that errors cannot be correlated. Here, we characterize a superconducting multiqubit circuit and find that charge fluctuations are highly correlated on a length scale over 600~μm; moreover, discrete charge jumps are accompanied by a strong transient suppression of qubit energy relaxation time across the millimeter-scale chip. The resulting correlated errors are explained in terms of the charging event and phonon-mediated quasiparticle poisoning associated with absorption of gamma rays and cosmic-ray muons in the qubit substrate. Robust quantum error correction will require the development of mitigation strategies to protect multiqubit arrays from correlated errors due to particle impacts.
arxiv pdf

Anomalous Charge Noise in Superconducting Qubits

  1. B. G. Christensen,
  2. C. D. Wilen,
  3. A. Opremcak,
  4. J. Nelson,
  5. F. Schlenker,
  6. C. H. Zimonick,
  7. L. Faoro,
  8. L.B. Ioffe,
  9. Y. J. Rosen,
  10. J. L. DuBois,
  11. B. L. T. Plourde,
  12. and R. McDermott
We have used Ramsey tomography to characterize charge noise in a weakly charge-sensitive superconducting qubit. We find a charge noise that scales with frequency as 1/fα over 5 decades
with α=1.93 and a magnitude Sq(1Hz)=2.9×10−4 e2/Hz. The noise exponent and magnitude of the low-frequency noise are much larger than those seen in prior work on single electron transistors, yet are consistent with reports of frequency noise in other superconducting qubits. Moreover, we observe frequent large-amplitude jumps in offset charge exceeding 0.1e; these large discrete charge jumps are incompatible with a picture of localized dipole-like two-level fluctuators. The data reveal an unexpected dependence of charge noise on device scale and suggest models involving either charge drift or fluctuating patch potentials.
arxiv pdf