update.555 (fwd)

[Jim Choate]

---------- Forwarded message ----------
Date: Thu, 6 Sep 2001 11:29:40 -0400 (EDT)
From: AIP listserver <physnews at aip.org>
To: physnews-mailing at aip.org
Subject: update.555


PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 555  September 6, 2001   by Phillip F. Schewe, Ben Stein,
and James Riordon

EVIDENCE FOR A RE-IONIZATION ERA in the early universe
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SUPERCONDUCTIVITY AT 117 K IN A BUCKYBALL CRYSTAL has been observed by
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LASER-LIKE AMPLIFICATION OF ENTANGLED PARTICLES has been achieved by a
University of Oxford team. Governed by quantum physics, entangled particles 
have much stronger correlations, or interrelationships, than anything
allowed in classical physics.  For example, measuring one entangled
particle instantly influences its partner's state, even if the two
particles are separated by great distances.  Entangled particles are
the bread-and-butter of quantum information schemes such as
quantum cryptography, quantum computing, and quantum
teleportation.  But they are notoriously difficult to create in bulk. 
To create entangled photons, for example, researchers can send
laser light through a barium borate crystal.  Passing through the
crystal, a photon sometimes splits into two entangled photons
(each with half the energy of the initial photon).  However, this
only occurs for one in every ten billion incoming photons. To
increase the yield, the Oxford researchers added a step: they put
mirrors beyond the crystal so that the laser pulse and entangled
pair could reflect, and have the chance to interact.  Since the
entangled pair and reflected laser pulse behave as waves, quantum
mechanics says that they could interfere constructively to generate
fourfold more two-photon pairs or interfere destructively to create
zero pairs.  Following these steps, the researchers increased
production of two-photon entangled pairs and also of rarer states
such as four-photon entangled quartets.  This achievement could
represent a step towards an entangled-photon laser, which would
repeatedly amplify entangled particles to create greater yields than
previously possible, and also towards the creation of new and more
complex kinds of entangled states.  (Lamas-Linares et al., Nature,
30 August 2001.)