Han Zheng

Syndrome-Resolved Decoding of Qubit Readout Errors

  1. Han Zheng,
  2. Vladimir Pešić,
  3. Nikolay Gusarov,
  4. Andrea Lizzit,
  5. Taketo Imaizumi,
  6. Chulwoo Ahn,
  7. Marco Nicolas Mueller,
  8. Raymond Mencia,
  9. Edoardo Charbon,
  10. and Vladimir E. Manucharyan
Readout errors in superconducting qubits include incorrect state assignment, bit flips within the computational subspace, and leakage to non-computational states. These errors require
different mitigation strategies, yet conventional measurement fidelity and repeatability metrics do not resolve their individual contributions. Previous repeated-readout studies have shown that temporal correlations reveal additional information about readout errors. Here we introduce the Readout Error Decoder (RED), which converts repeated thresholded binary records into a channel-resolved error budget. Controlled error injections validate the channel-specific response of the decoder. We demonstrate RED on both fluxonium and transmon qubits and across distinct leakage-lifetime regimes. RED identifies the error channels limiting readout performance without requiring dedicated discrimination of non-computational states, providing a basis for targeted readout optimization across different qubit modalities.
arxiv pdf

Coherent control of a few-channel hole type gatemon qubit

  1. Han Zheng,
  2. Luk Yi Cheung,
  3. Nikunj Sangwan,
  4. Artem Kononov,
  5. Roy Haller,
  6. Joost Ridderbos,
  7. Carlo Ciaccia,
  8. Jann Hinnerk Ungerer,
  9. Ang Li,
  10. Erik P.A.M. Bakkers,
  11. Andreas Baumgartner,
  12. and Christian Schönenberger
Gatemon qubits are the electrically tunable cousins of superconducting transmon qubits. In this work, we demonstrate the full coherent control of a gatemon qubit based on hole carriers
in a Ge/Si core/shell nanowire, with the longest coherence times in group IV material gatemons to date. The key to these results is a high-quality Josephson junction obtained in a straightforward and reproducible annealing technique. We demonstrate that the transport through the narrow junctions is dominated by only two quantum channels, with transparencies up to unity. This novel qubit platform holds great promise for quantum information applications, not only because it incorporates technologically relevant materials, but also because it provides new opportunities, like an ultrastrong spin-orbit coupling in the few-channel regime of Josephson junctions.
arxiv pdf