Ulysse Réglade

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

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.
arxiv pdf