Tzu-Chiao Chien

Demonstrating a superconducting dual-rail cavity qubit with erasure-detected logical measurements

  1. Kevin S. Chou,
  2. Tali Shemma,
  3. Heather McCarrick,
  4. Tzu-Chiao Chien,
  5. James D. Teoh,
  6. Patrick Winkel,
  7. Amos Anderson,
  8. Jonathan Chen,
  9. Jacob Curtis,
  10. Stijn J. de Graaf,
  11. John W.O. Garmon,
  12. Benjamin Gudlewski,
  13. William D. Kalfus,
  14. Trevor Keen,
  15. Nishaad Khedkar,
  16. Chan U Lei,
  17. Gangqiang Liu,
  18. Pinlei Lu,
  19. Yao Lu,
  20. Aniket Maiti,
  21. Luke Mastalli-Kelly,
  22. Nitish Mehta,
  23. Shantanu O. Mundhada,
  24. Anirudh Narla,
  25. Taewan Noh,
  26. Takahiro Tsunoda,
  27. Sophia H. Xue,
  28. Joseph O. Yuan,
  29. Luigi Frunzio,
  30. Jose Aumentado,
  31. Shruti Puri,
  32. Steven M. Girvin,
  33. S. Harvey Moseley Jr.,
  34. and Robert J. Schoelkopf
A critical challenge in developing scalable error-corrected quantum systems is the accumulation of errors while performing operations and measurements. One promising approach is to
design a system where errors can be detected and converted into erasures. A recent proposal aims to do this using a dual-rail encoding with superconducting cavities. In this work, we implement such a dual-rail cavity qubit and use it to demonstrate a projective logical measurement with erasure detection. We measure logical state preparation and measurement errors at the 0.01%-level and detect over 99% of cavity decay events as erasures. We use the precision of this new measurement protocol to distinguish different types of errors in this system, finding that while decay errors occur with probability ∼0.2% per microsecond, phase errors occur 6 times less frequently and bit flips occur at least 170 times less frequently. These findings represent the first confirmation of the expected error hierarchy necessary to concatenate dual-rail erasure qubits into a highly efficient erasure code.
arxiv pdf

A modular quantum computer based on a quantum state router

  1. Chao Zhou,
  2. Pinlei Lu,
  3. Matthieu Praquin,
  4. Tzu-Chiao Chien,
  5. Ryan Kaufman,
  6. Xi Cao,
  7. Mingkang Xia,
  8. Roger Mong,
  9. Wolfgang Pfaff,
  10. David Pekker,
  11. and Michael Hatridge
In this work, we present the design of a superconducting, microwave quantum state router which can realize all-to-all couplings among four quantum modules. Each module consists of a
single transmon, readout mode, and communication mode coupled to the router. The router design centers on a parametrically driven, Josephson-junction based three-wave mixing element which generates photon exchange among the modules‘ communication modes. We first demonstrate SWAP operations among the four communication modes, with an average full-SWAP time of 760 ns and average inter-module gate fidelity of 0.97, limited by our modes‘ coherences. We also demonstrate photon transfer and pairwise entanglement between the modules‘ qubits, and parallel operation of simultaneous SWAP gates across the router. These results can readily be extended to faster and higher fidelity router operations, as well as scaled to support larger networks of quantum modules.
arxiv pdf

Optimizing Josephson-Ring-Modulator-based Josephson Parametric Amplifiers via full Hamiltonian control

  1. Chenxu Liu,
  2. Tzu-Chiao Chien,
  3. Michael Hatridge,
  4. and David Pekker
Josephson Parametric Amplifiers (JPA) are nonlinear devices that are used for quantum sensing and qubit readout in the microwave regime. While JPAs regularly operate in the quantum
limit, their gain saturates for very small (few photon) input power. In a previous work, we showed that the saturation power of JPAs is not limited by pump depletion, but instead by the high-order nonlinearity of Josephson junctions, the nonlinear circuit elements that enables amplification in JPAs. Here, we present a systematic study of the nonlinearities in JPAs, we show which nonlinearities limit the saturation power, and present a strategy for optimizing the circuit parameters for achieving the best possible JPA. For concreteness, we focus on JPAs that are constructed around a Josephson Ring Modulator (JRM). We show that by tuning the external and shunt inductors, we should be able to take the best experimentally available JPAs and improve their saturation power by ∼15 dB. Finally, we argue that our methods and qualitative results are applicable to a broad range of cavity based JPAs.
arxiv pdf