Sponsored by
France-Chicago Center and College de France
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College de France and Ecole Normale Superieure, Paris
and
JFI Distinguished Visitor for 2007
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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
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