Special JFI Physics Colloquium

Sponsored by
  France-Chicago Center and College de France

Prof. Serge Haroche (bio.)

College de France and Ecole Normale Superieure, Paris
JFI Distinguished Visitor for 2007

Counting photons without destroying them:
an ideal measurement of light

Tuesday, October 2, 2007

4:00 pm, KPTC 106

followed by reception in KPTC 206 at 5:15 pm

While usual photo-detection procedures annihilate light quanta, we have developed a novel way to count photons without destroying them. A microwave field is stored between two highly reflecting mirrors for time intervals reaching half a second. A stream of very excited atoms pass, one at a time, between the mirrors. These atoms behave as microscopic clocks whose ticking rate is affected by light intensity. By measuring the clocks' delay, information is extracted from the field without any atomic energy absorption and the light progressively collapses into a state of well-defined photon number. This process satisfies all the criteria of an ideal quantum measurement. Residual absorption of photons in the mirrors results in quantum jumps, recorded as sudden changes of the photon number occurring at random times. This new way to "look" at light also leads to the preparation and manipulation of photonic "Schrodinger cats", which are coherent superpositions of field states with different phases or amplitudes, containing a large number of photons. The study of these states on fields trapped in one or two cavities opens new avenues for the exploration of the boundary between the quantum and classical worlds.

This event is free and open to the public.  Refreshment will be provided in KPTC 206 at 3:45pm.

Host: Cheng Chin and Tom Witten

The University of Chicago

This poster is on the internet at http://ultracold.uchicago.edu/haroche/colloquium.html