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  • Quantum state smoothing: why the types of observed and unobserved measurements matter

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    Chantasri214078-Published.pdf (2.298Mb)
    Author(s)
    Chantasri, Areeya
    Guevara, Ivonne
    Wiseman, Howard M
    Griffith University Author(s)
    Chantasri, Areeya
    Wiseman, Howard M.
    Guevara Prieto, Ivonne A.
    Year published
    2019
    Metadata
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    Abstract
    We investigate the estimation technique called quantum state smoothing introduced in (Guevara and Wiseman 2015 Phys. Rev. Lett. 115 180407), which offers a valid quantum state estimate for a partially monitored system, conditioned on the observed record both prior and posterior to an estimation time. The technique was shown to give a better estimate of the underlying true quantum states than the usual quantum filtering approach. However, the improvement in estimation fidelity, originally examined for a resonantly driven qubit coupled to two vacuum baths, was also shown to vary depending on the types of detection used for the ...
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    We investigate the estimation technique called quantum state smoothing introduced in (Guevara and Wiseman 2015 Phys. Rev. Lett. 115 180407), which offers a valid quantum state estimate for a partially monitored system, conditioned on the observed record both prior and posterior to an estimation time. The technique was shown to give a better estimate of the underlying true quantum states than the usual quantum filtering approach. However, the improvement in estimation fidelity, originally examined for a resonantly driven qubit coupled to two vacuum baths, was also shown to vary depending on the types of detection used for the qubit's fluorescence. In this work, we analyse this variation in a systematic way for the first time. We first define smoothing power using an average purity recovery and a relative average purity recovery, of smoothing over filtering. Then, we explore the power for various combinations of fluorescence detection for both observed and unobserved channels. We next propose a method to explain the variation of the smoothing power, based on multi-time correlation strength between fluorescence detection records. The method gives a prediction of smoothing power for different combinations, which is remarkably successful in comparison with numerically simulated qubit trajectories.
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    Journal Title
    New Journal of Physics
    Volume
    21
    Issue
    8
    DOI
    https://doi.org/10.1088/1367-2630/ab396e
    Copyright Statement
    © 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
    Subject
    Physical Sciences
    Science & Technology
    Physics, Multidisciplinary
    Physics
    quantum state estimation
    Publication URI
    http://hdl.handle.net/10072/388755
    Collection
    • Journal articles

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