S. Singh

Real-time quantum error correction beyond break-even

  1. V. V. Sivak,
  2. A. Eickbusch,
  3. B. Royer,
  4. S. Singh,
  5. I. Tsioutsios,
  6. S. Ganjam,
  7. A. Miano,
  8. B. L. Brock,
  9. A. Z. Ding,
  10. L. Frunzio,
  11. S. M. Girvin,
  12. R. J. Schoelkopf,
  13. and M. H. Devoret
The ambition of harnessing the quantum for computation is at odds with the fundamental phenomenon of decoherence. The purpose of quantum error correction (QEC) is to counteract the
natural tendency of a complex system to decohere. This cooperative process, which requires participation of multiple quantum and classical components, creates a special type of dissipation that removes the entropy caused by the errors faster than the rate at which these errors corrupt the stored quantum information. Previous experimental attempts to engineer such a process faced an excessive generation of errors that overwhelmed the error-correcting capability of the process itself. Whether it is practically possible to utilize QEC for extending quantum coherence thus remains an open question. We answer it by demonstrating a fully stabilized and error-corrected logical qubit whose quantum coherence is significantly longer than that of all the imperfect quantum components involved in the QEC process, beating the best of them with a coherence gain of G=2.27±0.07. We achieve this performance by combining innovations in several domains including the fabrication of superconducting quantum circuits and model-free reinforcement learning.
arxiv pdf

Cryogenic single-port calibration for superconducting microwave resonator measurements

  1. Haozhi Wang,
  2. S. Singh,
  3. C.R.H. McRae,
  4. J.C. Bardin,
  5. S.-X. Lin,
  6. N. Messaoudi,
  7. A.R. Castelli,
  8. Y. J. Rosen,
  9. E. T. Holland,
  10. D. P. Pappas,
  11. and J. Y. Mutus
Superconducting circuit testing and materials loss characterization requires robust and reliable methods for the extraction of internal and coupling quality factors of microwave resonators.
A common method, imposed by limitations on the device design or experimental configuration, is the single-port reflection geometry, i.e. reflection-mode. However, impedance mismatches in cryogenic systems must be accounted for through calibration of the measurement chain while it is at low temperatures. In this paper, we demonstrate a data-based, single-port calibration using commercial microwave standards and a vector network analyzer (VNA) with samples at millikelvin temperature in a dilution refrigerator, making this method useful for measurements of quantum phenomena. Finally, we cross reference our data-based, single-port calibration and reflection measurement with over-coupled 2D- and 3D-resonators against well established two-port techniques corroborating the validity of our method.
arxiv pdf