BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Quantum State Smoothing - Wiseman\, HM (Griffith University)
DTSTART:20140804T143000Z
DTEND:20140804T151000Z
UID:TALK53583@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Co-author: Ivonne Guevara (Griffith University) \n\nUnder nois
 y observations\, estimation theory allows one to infer the state of the me
 asured system\, if its a priori statistics are given. In the continuous ti
 me situation\, three different types of estimation can be distinguished: f
 iltering\, which is estimating of the state at time t from earlier records
 \; retro-filtering\, which is estimating the state at time t from later re
 cords\; and smoothing\, which is estimating the state at time t from both 
 earlier and later records. Of the three\, smoothing allows the greatest pr
 ecision. This theory has been well developed in classical systems\, but it
 s application to quantum systems has only recently begun to be explored. P
 revious works have used the term quantum smoothing to mean estimating clas
 sical parameters\, [Tsang\, Phys. Rev. Lett 102\, 250403 (2009)]\, which i
 s essentially classical smoothing in which the noisy observation of the cl
 assical parameters is mediated by a quantum system. Here we introduce quan
 tum state smoothin g\, where the state of a partially observed open quantu
 m system itself is smoothed. We achieve this by applying classical smoothi
 ng to a hypothetical unobserved noisy measurement record correlated with t
 he stochastic dynamics ("quantum trajectories") of the system\, induced by
  that hypothetical measurement. Using the formalism of linear quantum traj
 ectories\, we simulate quantum state smoothing for a simple system\, and s
 tudy how the choice of unravelling for the true observation of the system 
 affects how well the unobserved results can be estimated\, and hence how e
 ffective is the quantum state smoothing. Our investigations shed new light
  on the nature of open quantum systems and the applicability of classical 
 concepts.\n\n
LOCATION:Seminar Room 1\, Newton Institute
END:VEVENT
END:VCALENDAR