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.

Detecting itinerant microwave photons with engineered non-linear dissipation

  1. Raphaël Lescanne,
  2. Samuel Deléglise,
  3. Emanuele Albertinale,
  4. Ulysse Réglade,
  5. Thibault Capelle,
  6. Edouard Ivanov,
  7. Thibaut Jacqmin,
  8. Zaki Leghtas,
  9. and Emmanuel Flurin
Single photon detection is a key resource for sensing at the quantum limit and the enabling technology for measurement based quantum computing. Photon detection at optical frequencies
relies on irreversible photo-assisted ionization of various natural materials. However, microwave photons have energies 5 orders of magnitude lower than optical photons, and are therefore ineffective at triggering measurable phenomena at macroscopic scales. Here, we report the observation of a new type of interaction between a single two level system (qubit) and a microwave resonator. These two quantum systems do not interact coherently, instead, they share a common dissipative mechanism to a cold bath: the qubit irreversibly switches to its excited state if and only if a photon enters the resonator. We have used this highly correlated dissipation mechanism to detect itinerant photons impinging on the resonator. This scheme does not require any prior knowledge of the photon waveform nor its arrival time, and dominant decoherence mechanisms do not trigger spurious detection events (dark counts). We demonstrate a detection efficiency of 58% and a record low dark count rate of 1.4 per ms. This work establishes engineered non-linear dissipation as a key-enabling resource for a new class of low-noise non-linear microwave detectors.