Mysteries and Surprises in Quantum Physics
"Cavity quantum electrodynamics" is a sub-field of quantum optics..
Speaking at the EPL symposium, "Physics In Our Times" held last week
at the Fondation Del Duca de l'Institut de France, Paris Professor
Serge Haroche from the CollХge de France and the иcole Normale
SupИrieure in Paris, explained how he and his colleagues manipulate
and control single atoms and single photons interacting in a cavity,
which is a box made of highly reflecting walls.
By studying the behaviour of these atoms and photons in this protected
environment, the physicists can illustrate fundamental aspects of
quantum theory, such as state superpositions, complementarity and
decoherence. This research is related to the physics of quantum
information, a new domain at the frontier of information science and
physics that tries to harness the logic of the quantum world to
realise tasks in communication and computing that classical devices
"During the 20th century, quantum physics has given us new
technologies that have changed our lives - for example the computer,
the laser and magnetic resonance imaging to name a few," explained
Prof. Haroche. "However, quantum laws have counterintuitive aspects
that defy common sense. This has led to a paradox: although we all
take advantage of quantum physics, it remains very strange - even some
of the scientists that developed the theory, such as Einstein,
SchrЖdinger and de Broglie, were uneasy about its deep meaning," he said.
Prof. Haroche and his team have recently succeeded in trapping a
single photon in a box on the time scale of seconds and have detected
this photon many times without destroying it. The researchers have
achieved this by sending atoms across the box and measuring the
imprint left on the atoms by the photon. This is a new kind of light
detection called 'quantum non-demolition'," explained Prof. Haroche.
"Until now, single photons were always destroyed upon detection."
The result means that it is now possible repeatedly to extract
information from the same photon. This is important because the major
part of all information we get from the universe come from light.
"Developing a new way of 'seeing' could have applications in quantum
science," said Prof. Haroche. "A photon could share its information
with an ensemble of atoms to build up an 'entangled state' of light or
Attempting to manipulate and control quantum systems raises important
questions about the transition between quantum and classical
behaviour. "Fundamentally, the goal is to understand nature better,"
explained Prof. Haroche. "Applications, such as quantum communication
machines, will certainly come but what they will be useful for is not
yet clear. This is why research is so exciting - unpredictable things
keep happening all the time."
Prof. Haroche's group is currently working with atoms and photons in
cavities but related work is being done by other groups on trapped
ions and cold atoms in optical potential wells, with superconducting
junction or quantum dots in solid state devices. "Although the
technologies may differ widely, the quantum and information science
concepts used are the same," he explained. "We are therefore
witnessing a kind of unification between different fields of research
that is very promising."
Source: Institute of Physics
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