Enhancing dissipative cat qubit protection by squeezing

  1. Rémi Rousseau,
  2. Diego Ruiz,
  3. Emanuele Albertinale,
  4. Pol d'Avezac,
  5. Danielius Banys,
  6. Ugo Blandin,
  7. Nicolas Bourdaud,
  8. Giulio Campanaro,
  9. Gil Cardoso,
  10. Nathanael Cottet,
  11. Charlotte Cullip,
  12. Samuel Deléglise,
  13. Louise Devanz,
  14. Adam Devulder,
  15. Antoine Essig,
  16. Pierre Février,
  17. Adrien Gicquel,
  18. Élie Gouzien,
  19. Antoine Gras,
  20. Jérémie Guillaud,
  21. Efe Gümüş,
  22. Mattis Hallén,
  23. Anissa Jacob,
  24. Paul Magnard,
  25. Antoine Marquet,
  26. Salim Miklass,
  27. Théau Peronnin,
  28. Stéphane Polis,
  29. Felix Rautschke,
  30. Ulysse Réglade,
  31. Julien Roul,
  32. Jeremy Stevens,
  33. Jeanne Solard,
  34. Alexandre Thomas,
  35. Jean-Loup Ville,
  36. Pierre Wan-Fat,
  37. Raphaël Lescanne,
  38. Zaki Leghtas,
  39. Joachim Cohen,
  40. Sébastien Jezouin,
  41. and Anil Murani
Dissipative cat-qubits are a promising architecture for quantum processors due to their built-in quantum error correction. By leveraging two-photon stabilization, they achieve an exponentially
suppressed bit-flip error rate as the distance in phase-space between their basis states increases, incurring only a linear increase in phase-flip rate. This property substantially reduces the number of qubits required for fault-tolerant quantum computation. Here, we implement a squeezing deformation of the cat qubit basis states, further extending the bit-flip time while minimally affecting the phase-flip rate. We demonstrate a steep reduction in the bit-flip error rate with increasing mean photon number, characterized by a scaling exponent γ=4.3, rising by a factor of 74 per added photon. Specifically, we measure bit-flip times of 22 seconds for a phase-flip time of 1.3 μs in a squeezed cat qubit with an average photon number n¯=4.1, a 160-fold improvement in bit-flip time compared to a standard cat. Moreover, we demonstrate a two-fold reduction in Z-gate infidelity, with an estimated phase-flip probability of ϵX=0.085 and a bit-flip probability of ϵZ=2.65⋅10−9 which confirms the gate bias-preserving property. This simple yet effective technique enhances cat qubit performances without requiring design modification, moving multi-cat architectures closer to fault-tolerant quantum computation.

Energetics of a Single Qubit Gate

  1. Jeremy Stevens,
  2. Daniel Szombati,
  3. Maria Maffei,
  4. Cyril Elouard,
  5. Réouven Assouly,
  6. Nathanaël Cottet,
  7. Rémy Dassonneville,
  8. Quentin Ficheux,
  9. Stefan Zeppetzauer,
  10. Audrey Bienfait,
  11. Andrew N. Jordan,
  12. Alexia Auffèves,
  13. and Benjamin Huard
Qubits are physical, a quantum gate thus not only acts on the information carried by the qubit but also on its energy. What is then the corresponding flow of energy between the qubit
and the controller that implements the gate? Here we exploit a superconducting platform to answer this question in the case of a quantum gate realized by a resonant drive field. During the gate, the superconducting qubit becomes entangled with the microwave drive pulse so that there is a quantum superposition between energy flows. We measure the energy change in the drive field conditioned on the outcome of a projective qubit measurement. We demonstrate that the drive’s energy change associated with the measurement backaction can exceed by far the energy that can be extracted by the qubit. This can be understood by considering the qubit as a weak measurement apparatus of the driving field.