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  • Reconsidering rapid qubit purification by feedback

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    Author
    Wiseman, Howard
    Ralph, J.
    Year published
    2006
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    Abstract
    This paper reconsiders the claimed rapidity of a scheme for the purification of the quantum state of a qubit, proposed recently in Jacobs (2003 Phys. Rev. A 67 030301(R)). The qubit starts in a completely mixed state, and information is obtained by a continuous measurement. Jacobs' rapid purification protocol uses Hamiltonian feedback control to maximize the average purity of the qubit for a given time, with a factor of two increase in the purification rate over the no-feedback protocol. However, by re-examining the latter approach, we show that it minimizes the average time taken for a qubit to reach a given purity. In fact, ...
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    This paper reconsiders the claimed rapidity of a scheme for the purification of the quantum state of a qubit, proposed recently in Jacobs (2003 Phys. Rev. A 67 030301(R)). The qubit starts in a completely mixed state, and information is obtained by a continuous measurement. Jacobs' rapid purification protocol uses Hamiltonian feedback control to maximize the average purity of the qubit for a given time, with a factor of two increase in the purification rate over the no-feedback protocol. However, by re-examining the latter approach, we show that it minimizes the average time taken for a qubit to reach a given purity. In fact, the average time taken for the no-feedback protocol beats that for Jacobs' protocol by a factor of two. We discuss how this is compatible with Jacobs' result and the usefulness of the different approaches.
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    Journal Title
    New Journal of Physics
    Volume
    8
    Issue
    6
    Publisher URI
    http://www.iop.org/
    DOI
    https://doi.org/10.1088/1367-2630/8/6/090
    Copyright Statement
    © 2006 Institute of Physics. Reproduced in accordance with the copyright policy of the publisher. This journal is available online please use hypertext links.
    Note
    Page numbers are not for citation purposes. Instead, this article has the unique article number of 90.
    Publication URI
    http://hdl.handle.net/10072/12363
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