Characterization and Tomography of a Hidden Qubit

In circuit-based quantum computing the available gate set typically consists of single-qubit gates acting on each individual qubit and at least one entangling gate between pairs of qubits. In certain physical architectures, however, some qubits may be “hidden” and lacking direct addressability throu...

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Autores principales:	M. Pechal, G. Salis, M. Ganzhorn, D. J. Egger, M. Werninghaus, S. Filipp
Formato:	article
Lenguaje:	EN
Publicado:	American Physical Society 2021
Materias:	Physics QC1-999
Acceso en línea:	https://doaj.org/article/e9b35eca51334e8a839d2de90ad0df0c
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spelling	oai:doaj.org-article:e9b35eca51334e8a839d2de90ad0df0c2021-11-15T17:08:41ZCharacterization and Tomography of a Hidden Qubit10.1103/PhysRevX.11.0410322160-3308https://doaj.org/article/e9b35eca51334e8a839d2de90ad0df0c2021-11-01T00:00:00Zhttp://doi.org/10.1103/PhysRevX.11.041032http://doi.org/10.1103/PhysRevX.11.041032https://doaj.org/toc/2160-3308In circuit-based quantum computing the available gate set typically consists of single-qubit gates acting on each individual qubit and at least one entangling gate between pairs of qubits. In certain physical architectures, however, some qubits may be “hidden” and lacking direct addressability through dedicated control and readout lines, for instance, because of limited on-chip routing capabilities, or because the number of control lines becomes a limiting factor for many-qubit systems. In this case, no single-qubit operations can be applied to the hidden qubits and their state cannot be measured directly. Instead, they may be controlled and read out only via single-qubit operations on connected “control” qubits and a suitable set of two-qubit gates. We first discuss the impact of such restricted control capabilities on the performance of specific qubit coupling networks. We then experimentally demonstrate full control and measurement capabilities in a superconducting two-qubit device with local single-qubit control and iswap and controlled-phase two-qubit interactions enabled by a tunable coupler. We further introduce an iterative tune-up process required to completely characterize the gate set used for quantum process tomography and evaluate the resulting gate fidelities.M. PechalG. SalisM. GanzhornD. J. EggerM. WerninghausS. FilippAmerican Physical SocietyarticlePhysicsQC1-999ENPhysical Review X, Vol 11, Iss 4, p 041032 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Physics QC1-999
spellingShingle	Physics QC1-999 M. Pechal G. Salis M. Ganzhorn D. J. Egger M. Werninghaus S. Filipp Characterization and Tomography of a Hidden Qubit
description	In circuit-based quantum computing the available gate set typically consists of single-qubit gates acting on each individual qubit and at least one entangling gate between pairs of qubits. In certain physical architectures, however, some qubits may be “hidden” and lacking direct addressability through dedicated control and readout lines, for instance, because of limited on-chip routing capabilities, or because the number of control lines becomes a limiting factor for many-qubit systems. In this case, no single-qubit operations can be applied to the hidden qubits and their state cannot be measured directly. Instead, they may be controlled and read out only via single-qubit operations on connected “control” qubits and a suitable set of two-qubit gates. We first discuss the impact of such restricted control capabilities on the performance of specific qubit coupling networks. We then experimentally demonstrate full control and measurement capabilities in a superconducting two-qubit device with local single-qubit control and iswap and controlled-phase two-qubit interactions enabled by a tunable coupler. We further introduce an iterative tune-up process required to completely characterize the gate set used for quantum process tomography and evaluate the resulting gate fidelities.
format	article
author	M. Pechal G. Salis M. Ganzhorn D. J. Egger M. Werninghaus S. Filipp
author_facet	M. Pechal G. Salis M. Ganzhorn D. J. Egger M. Werninghaus S. Filipp
author_sort	M. Pechal
title	Characterization and Tomography of a Hidden Qubit
title_short	Characterization and Tomography of a Hidden Qubit
title_full	Characterization and Tomography of a Hidden Qubit
title_fullStr	Characterization and Tomography of a Hidden Qubit
title_full_unstemmed	Characterization and Tomography of a Hidden Qubit
title_sort	characterization and tomography of a hidden qubit
publisher	American Physical Society
publishDate	2021
url	https://doaj.org/article/e9b35eca51334e8a839d2de90ad0df0c
work_keys_str_mv	AT mpechal characterizationandtomographyofahiddenqubit AT gsalis characterizationandtomographyofahiddenqubit AT mganzhorn characterizationandtomographyofahiddenqubit AT djegger characterizationandtomographyofahiddenqubit AT mwerninghaus characterizationandtomographyofahiddenqubit AT sfilipp characterizationandtomographyofahiddenqubit
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Characterization and Tomography of a Hidden Qubit

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