A. Eickbusch

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

A stabilized logical quantum bit encoded in grid states of a superconducting cavity

  1. P. Campagne-Ibarcq,
  2. A. Eickbusch,
  3. S. Touzard,
  4. E. Zalys-Geller,
  5. N. E. Frattini,
  6. V. V. Sivak,
  7. P. Reinhold,
  8. S. Puri,
  9. S. Shankar,
  10. R. J. Schoelkopf,
  11. L. Frunzio,
  12. M. Mirrahimi,
  13. and M.H. Devoret
The majority of quantum information tasks require error-corrected logical qubits whose coherence times are vastly longer than that of currently available physical qubits. Among the
many quantum error correction codes, bosonic codes are particularly attractive as they make use of a single quantum harmonic oscillator to encode a correctable qubit in a hardware-efficient manner. One such encoding, based on grid states of an oscillator, has the potential to protect a logical qubit against all major physical noise processes. By stroboscopically modulating the interaction of a superconducting microwave cavity with an ancillary transmon, we have successfully prepared and permanently stabilized these grid states. The lifetimes of the three Bloch vector components of the encoded qubit are enhanced by the application of this protocol, and agree with a theoretical estimate based on the measured imperfections of the experiment.
arxiv pdf