Pavel Bushev

Parametric two-qubit gates via Landau-Zener interference

  1. Simon Geisert,
  2. Albert Hertel,
  3. Sören Ihssen,
  4. Zhongyi Jiang,
  5. Paul Kugler,
  6. Nicolas Zapata,
  7. Nicolas Gosling,
  8. Ameya Nambisan,
  9. Yuan Gao,
  10. Asier Galicia,
  11. Jéferson R. Guimarães,
  12. Yorgo Haddad,
  13. Marc Neis,
  14. Harsh Bhardwaj,
  15. Dmitriy A. Volkov,
  16. Juan Cereijo,
  17. Marcello Guardascione,
  18. Yebin Liu,
  19. Markus Jerger,
  20. Pavel Bushev,
  21. Frank Wilhelm-Mauch,
  22. Wolfgang Wernsdorfer,
  23. Shai Machnes,
  24. Mohammad Ansari,
  25. Rami Barends,
  26. and Ioan M. Pop
We propose and demonstrate gates between two superconducting qubits based on quantum interference of consecutive Landau-Zener (LZ) transitions. This gate mechanism bridges between baseband
and parametric two-qubit control, enabling in situ tuning of the control frequency across a continuous interval up to hundreds of MHz. Another advantage compared to dispersive couplers is that the speed of the LZ gate is on the order of the full coupling strength. We experimentally demonstrate the gate on two platforms, a modular chiplet architecture of coupled generalized flux qubits, and on a monolithic transmon architecture. The combination of tunability and gate speed establishes the LZ gate as a unique tool for multiplexing control pulses and interconnecting superconducting chiplet architectures.
arxiv pdf

Interfacing microwave qubits and optical photons via spin ensembles

  1. Susanne Blum,
  2. Christopher O'Brien,
  3. Nikolai Lauk,
  4. Pavel Bushev,
  5. Michael Fleischhauer,
  6. and Giovanna Morigi
A protocol is discussed which allows one to realize a transducer for single photons between the optical and the microwave frequency range. The transducer is a spin ensemble, where the
individual emitters possess both an optical and a magnetic-dipole transition. Reversible frequency conversion is realized by combining optical photon storage, by means of EIT, with the controlled switching of the coupling between the magnetic-dipole transition and a superconducting qubit, which is realized by means of a microwave cavity. The efficiency is quantified by the global fidelity for transferring coherently a qubit excitation between a single optical photon and the superconducting qubit. We test various strategies and show that the total efficiency is essentially limited by the optical quantum memory: It can exceed 80% for ensembles of NV centers and approaches 99% for cold atomic ensembles, assuming state-of-the-art experimental parameters. This protocol allows one to bridge the gap between the optical and the microwave regime so to efficiently combine superconducting and optical components in quantum networks.
arxiv pdf