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.

Repetition cat-qubits: fault-tolerant quantum computation with highly reduced overhead

  1. Jérémie Guillaud,
  2. and Mazyar Mirrahimi
Is it possible to reduce the complexity of quantum error correction close to that of a classical one? We present a repetition code based on the so-called cat-qubits as a viable approach
towards a massive reduction in the hardware requirements for universal and fault-tolerant quantum computation. The cat-qubits that are stabilized by a two-photon driven dissipative process, exhibit a tunable noise bias where the effective bit-flip errors are exponentially suppressed with the average number of photons. We propose a realization of a set of gates on the cat-qubits that preserve such a noise bias. Combining these base qubit operations, we build, at the level of the repetition cat-qubit, a universal set of fully protected logical gates. This set includes single qubit preparations and measurements, NOT, controlled-NOT and controlled-controlled-NOT (Toffoli) gates. Remarkably, this construction does not come with significant overhead as is the case with more conventional schemes requiring magic states preparation, distillation and injection. Finally, all required operations on the cat-qubits could be performed with simple modifications of existing experimental setups.