Chia-Chin Tsai

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

An All-van-der-Waals Qubit

  1. Sein Park,
  2. Sameia Zaman,
  3. Junghyun Kim,
  4. Junyoung An,
  5. Daniel Rodan-Legrain,
  6. Hung-Yu Tsao,
  7. Chia-Chin Tsai,
  8. Aranya Goswami,
  9. Réouven Assouly,
  10. William P. Banner,
  11. Gabriel D. Cutter,
  12. Kenji Watanabe,
  13. Takashi Taniguchi,
  14. Terry P. Orlando,
  15. Gil-Ho Lee,
  16. Kyle Serniak,
  17. Max Hays,
  18. Jeffrey A. Grover,
  19. Philip Kim,
  20. Pablo Jarillo-Herrero,
  21. Joel I.J. Wang,
  22. and William D. Oliver
Advances in solid-state physics, materials science, and device engineering have accelerated the development of superconducting qubits. Among emerging platforms, van der Waals (vdW)
materials and their heterostructures are potentially attractive building blocks for quantum devices, yet their realization in qubit architectures remains largely underexplored. Here we report an all-vdW superconducting qubit based on a NbSe2-hBN-NbSe2 junction, in which a thin hBN layer simultaneously provides Josephson coupling and capacitive shunting between two NbSe2 islands, forming a „merged-element“ transmon. Temporal characterization using circuit quantum electrodynamics (cQED) techniques yields an average energy-relaxation time T1,avg=55 μs, Hahn-echo coherence time T2E,avg=21 μs, and Ramsey coherence time T2R,avg=1.9 μs. The relatively low Ramsey time is primarily attributable to an enhanced sensitivity to charge noise consistent with the realized device parameters and not a fundamental limitation. These results show that lumped-element superconducting qubits based on vdW heterostructures can achieve coherence times comparable to those of conventional Al-AlOx-Al qubits, while offering a reduced device footprint and suppressed stray capacitive coupling.
arxiv pdf