Paul Kugler

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

Probing the memory of a superconducting qubit environment

  1. Nicolas Gosling,
  2. Denis Bénâtre,
  3. Nicolas Zapata,
  4. Paul Kugler,
  5. Mitchell Field,
  6. Sumeru Hazra,
  7. Simon Günzler,
  8. Thomas Reisinger,
  9. Martin Spiecker,
  10. Mathieu Féchant,
  11. and Ioan M. Pop
Achieving fault tolerance with superconducting quantum processors requires qubits to operate within the regime of threshold theorems based on the Born-Markov approximation. This approximation,
which models dissipation as constant energy decay into a memoryless environment, breaks down when qubits couple to long-lived two-level systems (TLSs) that become polarized during operation and retain memory of past qubit states. Here, we show that non-Poissonian quantum jump traces carry the information required to distinguish long-lived TLSs from the standard Markovian bath. By fitting the Solomon equations to measured quantum jumps dynamics arising naturally due to thermal fluctuations, we can disentangle the coupling of the qubit to the two environments. Sweeping the qubit frequency reveals distinct peaks, each associated with a TLS that outlives the qubit, providing a handle to understand their microscopic origin.
arxiv pdf