Transmon qubit readout fidelity at the threshold for quantum error correction without a quantum-limited amplifier

Liangyu Chen*, Hang Xi Li, Yong Lu, Christopher W. Warren, Christian J. Križan, Sandoko Kosen, Marcus Rommel, Shahnawaz Ahmed, Amr Osman, Janka Biznárová, Anita Fadavi Roudsari, Benjamin Lienhard, Marco Caputo, Kestutis Grigoras, Leif Grönberg, Joonas Govenius, Anton Frisk Kockum, Per Delsing, Jonas Bylander*, Giovanna Tancredi*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

50 Citations (Scopus)

Abstract

High-fidelity and rapid readout of a qubit state is key to quantum computing and communication, and it is a prerequisite for quantum error correction. We present a readout scheme for superconducting qubits that combines two microwave techniques: applying a shelving technique to the qubit that reduces the contribution of decay error during readout, and a two-tone excitation of the readout resonator to distinguish among qubit populations in higher energy levels. Using a machine-learning algorithm to post-process the two-tone measurement results further improves the qubit-state assignment fidelity. We perform single-shot frequency-multiplexed qubit readout, with a 140 ns readout time, and demonstrate 99.5% assignment fidelity for two-state readout and 96.9% for three-state readout–without using a quantum-limited amplifier.

Original languageEnglish
Article number26
Number of pages7
JournalNPJ Quantum Information
Volume9
Issue number1
DOIs
Publication statusPublished - Mar 2023
MoE publication typeA1 Journal article-refereed

Funding

We would like to thank Daryoush Shiri for valuable discussions on microwave theory and simulation. The fabrication of our quantum processor was performed in part at Myfab Chalmers and flip-chip integration was done at VTT. We are grateful to the Quantum Device Lab at ETH Zürich for sharing their designs of the printed circuit board and sample holder. The device simulations were enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC) at National Supercomputer Centre (NSC) partially funded by the Swedish Research Council through grant agreement no. 2018-05973. This research was financially supported by the Knut and Alice Wallenberg Foundation through the Wallenberg Center for Quantum Technology (WACQT), the Swedish Research Council, and the EU Flagship on Quantum Technology H2020-FETFLAG-2018-03 project 820363 OpenSuperQ.

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