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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-3877
DTSTART:20160129T210000Z
DTEND:20160129T220000Z
DTSTAMP:20260419T174009Z
LAST-MODIFIED:20160121T151358Z
LOCATION:2241 Chamberlin Hall
SUMMARY:Quantum trajectories and the quantum state of the past\, Physi
 cs Department Colloquium\, Klaus Molmer\, Aarhus University
DESCRIPTION:The state of a quantum system is described by a wavefuncti
 on evolving in time according to the Schroedinger equation. If a measu
 rement is carried out on the system\, its wave function collapses\, i.
 e.\, it changes according to the random outcome of the measurement. Du
 ring a sequence of measurements on a single system\, its quantum state
  thus follows a stochastic trajectory in which the normal quantum mech
 anical time evolution is interrupted by collapses at each measurement.
 <br>
\n<br>
\nThe resulting state of the system\, at any time\, succes
 sfully predicts probabilities and mean values for the measurement of p
 hysical observables. In this talk we ask whether the sequence of measu
 rements also adds to our knowledge about the state of the system at ea
 rlier times during the experiment.<br>
\n<br>
\nThe answer is yes\, an
 d I shall show how such "hindsight" knowledge can be formally defined 
 in quantum mechanics and how we can represent it via a time evolving (
 past) state\, which at any time depends on both earlier and later meas
 urement outcomes. I will show applications of the theory to experiment
 s on atoms and superconducting qubits\, and I will discuss how the con
 cept and formalism of past quantum states touch upon both practical an
 d foundational aspects of quantum physics.
URL:https://www.physics.wisc.edu/events/?id=3877
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