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CATEGORIES:Isaac Newton Institute Seminar Series
SUMMARY:Quantum State Smoothing - Wiseman\, HM (Griffith U
niversity)
DTSTART;TZID=Europe/London:20140804T153000
DTEND;TZID=Europe/London:20140804T161000
UID:TALK53583AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/53583
DESCRIPTION:Co-author: Ivonne Guevara (Griffith University) \n
\nUnder noisy observations\, estimation theory all
ows one to infer the state of the measured system\
, if its a priori statistics are given. In the con
tinuous time situation\, three different types of
estimation can be distinguished: filtering\, which
is estimating of the state at time t from earlier
records\; retro-filtering\, which is estimating t
he state at time t from later records\; and smooth
ing\, which is estimating the state at time t from
both earlier and later records. Of the three\, sm
oothing allows the greatest precision. This theory
has been well developed in classical systems\, bu
t its application to quantum systems has only rece
ntly begun to be explored. Previous works have use
d the term quantum smoothing to mean estimating cl
assical parameters\, [Tsang\, Phys. Rev. Lett 102\
, 250403 (2009)]\, which is essentially classical
smoothing in which the noisy observation of the cl
assical parameters is mediated by a quantum system
. Here we introduce quantum state smoothin g\, whe
re the state of a partially observed open quantum
system itself is smoothed. We achieve this by appl
ying classical smoothing to a hypothetical unobser
ved noisy measurement record correlated with the s
tochastic dynamics ("quantum trajectories") of the
system\, induced by that hypothetical measurement
. Using the formalism of linear quantum trajectori
es\, we simulate quantum state smoothing for a sim
ple system\, and study how the choice of unravelli
ng for the true observation of the system affects
how well the unobserved results can be estimated\,
and hence how effective is the quantum state smoo
thing. Our investigations shed new light on the na
ture of open quantum systems and the applicability
of classical concepts.\n\n
LOCATION:Seminar Room 1\, Newton Institute
CONTACT:Mustapha Amrani
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