High-Fidelity Measurement of Qubits Encoded in Multilevel Superconducting Circuits

Qubit measurements are central to quantum information processing. In the field of superconducting qubits, standard readout techniques are limited not only by the signal-to-noise ratio, but also by state relaxation during the measurement. In this work, we demonstrate that the limitation due to relaxa...

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Autores principales:	Salvatore S. Elder, Christopher S. Wang, Philip Reinhold, Connor T. Hann, Kevin S. Chou, Brian J. Lester, Serge Rosenblum, Luigi Frunzio, Liang Jiang, Robert J. Schoelkopf
Formato:	article
Lenguaje:	EN
Publicado:	American Physical Society 2020
Materias:	Physics QC1-999
Acceso en línea:	https://doaj.org/article/d8d78fc8871c4fcba325384b109124f3
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spelling	oai:doaj.org-article:d8d78fc8871c4fcba325384b109124f32021-12-02T12:07:29ZHigh-Fidelity Measurement of Qubits Encoded in Multilevel Superconducting Circuits10.1103/PhysRevX.10.0110012160-3308https://doaj.org/article/d8d78fc8871c4fcba325384b109124f32020-01-01T00:00:00Zhttp://doi.org/10.1103/PhysRevX.10.011001http://doi.org/10.1103/PhysRevX.10.011001https://doaj.org/toc/2160-3308Qubit measurements are central to quantum information processing. In the field of superconducting qubits, standard readout techniques are limited not only by the signal-to-noise ratio, but also by state relaxation during the measurement. In this work, we demonstrate that the limitation due to relaxation can be suppressed by using the many-level Hilbert space of superconducting circuits: In a multilevel encoding, the measurement is corrupted only when multiple errors occur. Employing this technique, we show that we can directly resolve transmon gate errors at the level of one part in 10^{3}. Extending this idea, we apply the same principles to the measurement of a logical qubit encoded in a bosonic mode and detected with a transmon ancilla, implementing a proposal by Hann et al. [Phys. Rev. A 98, 022305 (2018)PLRAAN2469-992610.1103/PhysRevA.98.022305]. Qubit state assignments are made based on a sequence of repeated readouts, further reducing the overall infidelity. This approach is quite general, and several encodings are studied; the codewords are more distinguishable when the distance between them is increased with respect to photon loss. The trade-off between multiple readouts and state relaxation is explored and shown to be consistent with the photon-loss model. We report a logical assignment infidelity of 5.8×10^{-5} for a Fock-based encoding and 4.2×10^{-3} for a quantum error correction code (the S=2, N=1 binomial code). Our results not only improve the fidelity of quantum information applications, but also enable more precise characterization of process or gate errors.Salvatore S. ElderChristopher S. WangPhilip ReinholdConnor T. HannKevin S. ChouBrian J. LesterSerge RosenblumLuigi FrunzioLiang JiangRobert J. SchoelkopfAmerican Physical SocietyarticlePhysicsQC1-999ENPhysical Review X, Vol 10, Iss 1, p 011001 (2020)
institution	DOAJ
collection	DOAJ
language	EN
topic	Physics QC1-999
spellingShingle	Physics QC1-999 Salvatore S. Elder Christopher S. Wang Philip Reinhold Connor T. Hann Kevin S. Chou Brian J. Lester Serge Rosenblum Luigi Frunzio Liang Jiang Robert J. Schoelkopf High-Fidelity Measurement of Qubits Encoded in Multilevel Superconducting Circuits
description	Qubit measurements are central to quantum information processing. In the field of superconducting qubits, standard readout techniques are limited not only by the signal-to-noise ratio, but also by state relaxation during the measurement. In this work, we demonstrate that the limitation due to relaxation can be suppressed by using the many-level Hilbert space of superconducting circuits: In a multilevel encoding, the measurement is corrupted only when multiple errors occur. Employing this technique, we show that we can directly resolve transmon gate errors at the level of one part in 10^{3}. Extending this idea, we apply the same principles to the measurement of a logical qubit encoded in a bosonic mode and detected with a transmon ancilla, implementing a proposal by Hann et al. [Phys. Rev. A 98, 022305 (2018)PLRAAN2469-992610.1103/PhysRevA.98.022305]. Qubit state assignments are made based on a sequence of repeated readouts, further reducing the overall infidelity. This approach is quite general, and several encodings are studied; the codewords are more distinguishable when the distance between them is increased with respect to photon loss. The trade-off between multiple readouts and state relaxation is explored and shown to be consistent with the photon-loss model. We report a logical assignment infidelity of 5.8×10^{-5} for a Fock-based encoding and 4.2×10^{-3} for a quantum error correction code (the S=2, N=1 binomial code). Our results not only improve the fidelity of quantum information applications, but also enable more precise characterization of process or gate errors.
format	article
author	Salvatore S. Elder Christopher S. Wang Philip Reinhold Connor T. Hann Kevin S. Chou Brian J. Lester Serge Rosenblum Luigi Frunzio Liang Jiang Robert J. Schoelkopf
author_facet	Salvatore S. Elder Christopher S. Wang Philip Reinhold Connor T. Hann Kevin S. Chou Brian J. Lester Serge Rosenblum Luigi Frunzio Liang Jiang Robert J. Schoelkopf
author_sort	Salvatore S. Elder
title	High-Fidelity Measurement of Qubits Encoded in Multilevel Superconducting Circuits
title_short	High-Fidelity Measurement of Qubits Encoded in Multilevel Superconducting Circuits
title_full	High-Fidelity Measurement of Qubits Encoded in Multilevel Superconducting Circuits
title_fullStr	High-Fidelity Measurement of Qubits Encoded in Multilevel Superconducting Circuits
title_full_unstemmed	High-Fidelity Measurement of Qubits Encoded in Multilevel Superconducting Circuits
title_sort	high-fidelity measurement of qubits encoded in multilevel superconducting circuits
publisher	American Physical Society
publishDate	2020
url	https://doaj.org/article/d8d78fc8871c4fcba325384b109124f3
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_version_	1718394719001640960

High-Fidelity Measurement of Qubits Encoded in Multilevel Superconducting Circuits

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