Dual-rail encoding with superconducting cavities

  1. James D. Teoh,
  2. Patrick Winkel,
  3. Harshvardhan K. Babla,
  4. Benjamin J. Chapman,
  5. Jahan Claes,
  6. Stijn J. de Graaf,
  7. John W.O. Garmon,
  8. William D. Kalfus,
  9. Yao Lu,
  10. Aniket Maiti,
  11. Kaavya Sahay,
  12. Neel Thakur,
  13. Takahiro Tsunoda,
  14. Sophia H. Xue,
  15. Luigi Frunzio,
  16. Steven M. Girvin,
  17. Shruti Puri,
  18. and Robert J. Schoelkopf
The design of quantum hardware that reduces and mitigates errors is essential for practical quantum error correction (QEC) and useful quantum computations. To this end, we introduce the circuit-QED dual-rail qubit in which our physical qubit is encoded in the single-photon subspace of two superconducting cavities. The dominant photon loss errors can be detected and converted into erasure errors, which are much easier to correct. In contrast to linear optics, a circuit-QED implementation of the dual-rail code offers completely new capabilities. Using a single transmon ancilla, we describe a universal gate set that includes state preparation, logical readout, and parametrizable single and two-qubit gates. Moreover, first-order hardware errors due to the cavity and transmon in all of these operations can be detected and converted to erasure errors, leaving background Pauli errors that are orders of magnitude smaller. Hence, the dual-rail cavity qubit delivers an optimal hierarchy of errors and rates, and is expected to be well below the relevant QEC thresholds with today’s devices.
arxiv pdf

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