Sensitivity and back action in charge qubit measurements by a strongly coupled single-electron transistor

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Title Sensitivity and back action in charge qubit measurements by a strongly coupled single-electron transistor
Author Oxtoby, Neil Paul; Wiseman, Howard Mark; Sun, He-Bi
Journal Name Physical Review B: Condensed Matter and Materials Physics
Year Published 2006
Place of publication Ridge, NY
Publisher American Physical Society
Abstract We consider charge-qubit monitoring (continuous-in-time weak measurement) by a single-electron transistor (SET) operating in the sequential-tunneling regime. We show that commonly used master equations for this regime are not of the Lindblad form that is necessary and sufficient for guaranteeing valid physical states. In this paper we derive a Lindblad-form master equation and a corresponding quantum trajectory model for continuous measurement of the charge qubit by a SET. Our approach requires that the SET-qubit coupling be strong compared to the SET tunnelling rates. We present an analysis of the quality of the qubit measurement in this model (sensitivity versus back-action). Typically, the strong coupling when the SET island is occupied causes back-action on the qubit beyond the quantum back-action necessary for its sensitivity, and hence the conditioned qubit state is mixed. However, in one strongly coupled, asymmetric regime, the SET can approach the limit of an ideal detector with an almost pure conditioned state. We also quantify the quality of the SET using more traditional concepts such as the measurement time and decoherence time, which we have generalized so as to treat the strongly responding regime.
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Published Yes
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Copyright Statement Copyright 2006 American Physical Society. This is the author-manuscript version of this paper. Reproduced in accordance with the copyright policy of the publisher. Please refer to the journal's website for access to the definitive, published version.
Volume 74
Page from 045328.01
Page to 045328.11
ISSN 1098-0121
Date Accessioned 2007-03-09
Language en_AU
Research Centre Centre for Quantum Dynamics
Faculty Faculty of Science, Environment, Engineering and Technology
Subject PRE2009-Theoretical Physics
Publication Type Journal Articles (Refereed Article)
Publication Type Code c1

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