Fast, High-Fidelity Erasure Detection of Dual-Rail Qubits with Symmetrically Coupled Readout

  1. Jimmy Shih-Chun Hung,
  2. Arbel Haim,
  3. Mouktik Raha,
  4. Gihwan Kim,
  5. Ziwen Huang,
  6. Ming-Han Chou,
  7. Mitch D'Ewart,
  8. Erik Davis,
  9. Anurag Mishra,
  10. Patricio Arrangoiz-Arriola,
  11. Amirhossein Khalajhedayati,
  12. David Hover,
  13. Fernando G.S.L. Brandão,
  14. Aashish A. Clerk,
  15. Alex Retzker,
  16. Harry Levine,
  17. and Oskar Painter
Erasure qubits are a promising platform for implementing hardware-efficient quantum error correction. Realizing the error-correction advantages of this encoding requires frequent mid-circuit erasure checks that are fast, high-fidelity, and scalable. Here, we realize erasure detection with a hardware-efficient circuit consisting of a single readout resonator dispersively and symmetrically coupled to both transmons of a dual-rail qubit. We use this circuit to demonstrate single-shot erasure detection in 384 ns with minimal impact on the dual-rail logical manifold, achieving a residual error per check of 6.0(2)×10−4, with only 8(3)×10−5 induced dephasing per check, and an erasure error per check of 2.54(1)×10−2. The high degree of matched dispersive readout coupling (χ-matching) within the dual-rail qubit code space also allows us to realize a new modality: time-continuous erasure detection performed in parallel with single-qubit gates. Here we achieve a median 7.2×10−5 error per gate with <1×10−5 error induced by erasure detection. This demonstrates a reduction in erasure detection overhead as well as a crucial ingredient for soft information quantum error correction. Together, these results establish symmetrically coupled dispersive readout as a fast, hardware-efficient, and scalable component for erasure-based quantum error correction using transmon dual-rail qubits.
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