Lev-Arcady Sellem

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

A GKP qubit protected by dissipation in a high-impedance superconducting circuit driven by a microwave frequency comb

  1. Lev-Arcady Sellem,
  2. Alain Sarlette,
  3. Zaki Leghtas,
  4. Mazyar Mirrahimi,
  5. Pierre Rouchon,
  6. and Philippe Campagne-Ibarcq
We propose a novel approach to generate, protect and control GKP qubits. It employs a microwave frequency comb parametrically modulating a Josephson circuit to enforce a dissipative
dynamics of a high impedance circuit mode, autonomously stabilizing the finite-energy GKP code. The encoded GKP qubit is robustly protected against all dominant decoherence channels plaguing superconducting circuits but quasi-particle poisoning. In particular, noise from ancillary modes leveraged for dissipation engineering does not propagate at the logical level. In a state-of-the-art experimental setup, we estimate that the encoded qubit lifetime could extend two orders of magnitude beyond the break-even point, with substantial margin for improvement through progress in fabrication and control electronics. Qubit initialization, readout and control via Clifford gates can be performed while maintaining the code stabilization, paving the way toward the assembly of GKP qubits in a fault-tolerant quantum computing architecture.
arxiv pdf