Mattis Hallén

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.
arxiv pdf

Quantum control of a cat-qubit with bit-flip times exceeding ten seconds

  1. Ulysse Réglade,
  2. Adrien Bocquet,
  3. Ronan Gautier,
  4. Antoine Marquet,
  5. Emanuele Albertinale,
  6. Natalia Pankratova,
  7. Mattis Hallén,
  8. Felix Rautschke,
  9. Lev-Arcady Sellem,
  10. Pierre Rouchon,
  11. Alain Sarlette,
  12. Mazyar Mirrahimi,
  13. Philippe Campagne-Ibarcq,
  14. Raphaël Lescanne,
  15. Sébastien Jezouin,
  16. and Zaki Leghtas
Binary classical information is routinely encoded in the two metastable states of a dynamical system. Since these states may exhibit macroscopic lifetimes, the encoded information inherits
a strong protection against bit-flips. A recent qubit – the cat-qubit – is encoded in the manifold of metastable states of a quantum dynamical system, thereby acquiring bit-flip protection. An outstanding challenge is to gain quantum control over such a system without breaking its protection. If this challenge is met, significant shortcuts in hardware overhead are forecast for quantum computing. In this experiment, we implement a cat-qubit with bit-flip times exceeding ten seconds. This is a four order of magnitude improvement over previous cat-qubit implementations, and six orders of magnitude enhancement over the single photon lifetime that compose this dynamical qubit. This was achieved by introducing a quantum tomography protocol that does not break bit-flip protection. We prepare and image quantum superposition states, and measure phase-flip times above 490 nanoseconds. Most importantly, we control the phase of these superpositions while maintaining the bit-flip time above ten seconds. This work demonstrates quantum operations that preserve macroscopic bit-flip times, a necessary step to scale these dynamical qubits into fully protected hardware-efficient architectures.
arxiv pdf