Shoumik D. Chowdhury

Bosonic Error Correction with Fluxonium

  1. Shantanu R. Jha,
  2. Shoumik D. Chowdhury,
  3. Gabriele Rolleri,
  4. Anaida Ali,
  5. Lev-Arcady Sellem,
  6. Réouven Assouly,
  7. David Pahl,
  8. Lukas Pahl,
  9. Junyoung An,
  10. Farid Hassani,
  11. Hung-Yu Tsao,
  12. Chia-Chin Tsai,
  13. Aranya Goswami,
  14. Jeremie Boudreault,
  15. Jeffrey M. Gertler,
  16. Michael A. Gingras,
  17. Bethany M. Niedzielski,
  18. Jeffrey M. Knecht,
  19. Mollie E. Schwartz,
  20. Kyle Serniak,
  21. Jeffrey A. Grover,
  22. Baptiste Royer,
  23. Max Hays,
  24. and William D. Oliver
Bosonic quantum error correction (QEC) offers a hardware-efficient route to fault-tolerant quantum computing. To date, however, superconducting circuit implementations of bosonic codes
have utilized centimeter-scale 3D microwave cavities controlled by fixed-frequency transmon qubits, with logical lifetimes limited by transmon bit-flip errors. Here, we realize bosonic QEC in a fully planar architecture by pairing a heavy fluxonium, whose 451±70 μs bit-flip lifetime exceeds that of any control qubit in previous demonstrations, with an on-chip Archimedean spiral resonator several orders of magnitude smaller in mode volume than prior 3D cavities. We prepare finite-energy Gottesman-Kitaev-Preskill (GKP) states and stabilize them using measurement-free error correction with rapid fluxonium reset, extending the logical lifetime by a factor of 1.59±0.05. These results provide the first demonstration of resonator control using a weakly coupled fluxonium and, with it, the first realization of standalone bosonic QEC in a fully planar superconducting circuit architecture.
arxiv pdf

Bosonic quantum control with a weakly coupled fluxonium qubit

  1. Anaida Ali,
  2. Shantanu R. Jha,
  3. Shoumik D. Chowdhury,
  4. Lev-Arcady Sellem,
  5. Max Hays,
  6. William D. Oliver,
  7. and Baptiste Royer
Echoed Conditional Displacement (ECD) gates constitute a fundamental building block for quantum control of harmonic oscillator modes. However, bit-flips of the auxiliary qubit remain
a dominant error mechanism for this kind of bosonic control. In this work, we present a numerical case study of a bit-flip protected fluxonium operating as the control qubit and numerically implement ECD gates in a single-mode resonator-fluxonium device, demonstrating that fidelities exceeding 99.9% are possible. We systematically investigate the resonator dynamics using a combination of semiclassical trajectories and master equation simulations, numerically revealing asymptotic saturation of the dispersive shift in the strongly driven regime of the resonator. We develop an efficient technique to numerically simulate the strongly driven regime of the resonator using a semiclassical formulation that maps the full perturbation series in the dispersive expansion as order-by-order frequency shifts. This provides a compact polynomial description of the resonator which is intuitive and remains valid throughout the dispersive regime. Furthermore, we propose an improved ECD sequence that accounts for the effects of photon loss and spurious nonlinear terms on resonator trajectories.
arxiv pdf