Jimmy Shih-Chun Hung

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-circuiterasure 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.[/expand]
arxiv pdf

Readout-induced degradation of transmon lifetimes: interplay of TLSs and qubit spectral reshaping

  1. Ziwen Huang,
  2. Jimmy Shih-Chun Hung,
  3. Mouktik Raha,
  4. Ming-Han Chou,
  5. Harry Levine,
  6. Alex Retzker,
  7. Connor T. Hann,
  8. David Hover,
  9. Fernando G.S.L. Brandão,
  10. Aashish A. Clerk,
  11. Arbel Haim,
  12. and Oskar Painter
Measurement backaction degrades dispersive readout of superconducting qubits even at modest drive strengths, often via the reduction of qubit lifetimes during readout. In this work,
we theoretically and experimentally study this degradation and show how it can result from the interplay between detuned two-level systems (TLSs) and a drive-renormalized qubit spectrum. For modest to strong readout, the qubit emission spectrum becomes non-Lorentzian and depends sensitively on the readout drive frequency (even when measurement rate is fixed). We combine the readout-modified qubit emission spectrum with time-dependent perturbation theory to predict qubit lifetimes in the presence of a TLS bath. Master equation simulations and experimental measurements on a frequency-tunable transmon confirm these predictions quantitatively. In particular, we find that driving at the resonator frequency associated with the qubit ground state yields the narrowest qubit emission spectrum and the least lifetime degradation for a fixed measurement rate, providing a practical guideline for optimizing readout protocols in future quantum processors.
arxiv pdf