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 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.
Highlights
Theories for open quantum systems and quantum measurements [1,2,3,4,5,6] developed during the past decades are becoming standard tools in analysing and designing experiments for quantum technologies
We propose a method to explain the variation of the smoothing power, based on multitime correlation strength between fluorescence detection records
We have investigated quantum state smoothing [29], for a resonantly driven qubit coupled to bosonic baths, concentrating on calculating how much the smoothing helps improve the quality of state estimation over the filtering
Summary
We investigate the estimation technique called quantum state smoothing introduced in 115 180407), which offers a valid quantum state estimate for a partially this work must maintain attribution to the monitored system, conditioned on the observed record both prior and posterior to an estimation author(s) and the title of time. The technique was shown to give a better estimate of the underlying true quantum states than the work, journal citation and DOI. The improvement in estimation fidelity, originally examined for a resonantly driven qubit coupled to two vacuum baths, was shown to vary depending on the types of detection used for the qubit’s fluorescence. We propose a method to explain the variation of the smoothing power, based on multitime correlation strength between fluorescence detection records.
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