High-fidelity feedback-assisted parity measurement in circuit QED

L. Tornberg and G. Johansson
Phys. Rev. A 82, 012329 – Published 26 July 2010

Abstract

We analyze a two-qubit parity measurement based on dispersive readout in circuit quantum electrodynamics. The back action on the qubits has two qualitatively different contributions. One is an unavoidable dephasing in one of the parity subspaces, arising during the transient time of switching on the measurement. The other part is a stochastic rotation of the phase in the same subspace, which persists during the whole measurement. The latter can be determined from the full measurement record using the method of state estimation. Our main result is that the outcome of this phase determination process is independent of the initial state in the state estimation procedure. The procedure can thus be used in a measurement situation where the initial state is unknown. We discuss how this feedback method can be used to achieve a high-fidelity parity measurement for moderate values of the cavity-qubit coupling strength. Finally, we discuss the robustness of the feedback procedure toward errors in the measurement record.

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  • Received 29 March 2010

DOI:https://doi.org/10.1103/PhysRevA.82.012329

©2010 American Physical Society

Authors & Affiliations

L. Tornberg and G. Johansson

  • Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, SE-41296 Gothenburg, Sweden

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Vol. 82, Iss. 1 — July 2010

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