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PRODID:UW-Madison-Physics-Events
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UID:UW-Physics-Event-1090
DTSTART:20080411T210000Z
DURATION:PT1H0M0S
DTSTAMP:20260423T041113Z
LAST-MODIFIED:20080319T151319Z
LOCATION:2241 Chamberlin Hall (coffee at 3:30 pm)
SUMMARY:Trapping and Counting Photons without Destroying Them: A New W
 ay to Look at Light\, Physics Department Colloquium\, Serge Haroche\, 
 Ecole Normale Superieure
DESCRIPTION:An experiment realizing a quantum non-demolition measureme
 nt of a microwave field trapped in a cavity will be described. While u
 sual photo-detection destroys light quanta\, we have developed a new w
 ay to count  photons without absorbing them\, making it possible to me
 asure the same field repeatedly. We use as detectors atoms prepared in
  a superposition of Rydberg states which cross the cavity one at a tim
 e and behave as microscopic clocks whose ticking rate is affected by l
 ight. By measuring the clocks' delay\, information is extracted withou
 t energy absorption and the field progressively collapses into a well-
 defined photon number state. Quantum jumps between decreasing photon n
 umbers are recorded as the cavity field subsequently relaxes towards v
 acuum. This new way to "look" at light also generates coherent superpo
 sitions of photonic states with different phases called "Schroedinger 
 cats". By monitoring the evolution of these states\, we directly obser
 ve the process of decohere once in experiments opening new avenues for
  the exploration of the boundary between the quantum and classical wor
 lds. 
URL:https://www.physics.wisc.edu/events/?id=1090
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