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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 560 October 9, 2001 by Phillip F. Schewe, Ben Stein, and
James Riordon
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THE 2001 NOBEL PRIZE IN PHYSICS goes to Eric Cornell of
NIST/JILA, Wolfgang Ketterle of MIT, and Carl Wieman of
Colorado/JILA (JILA is an institute run jointly by NIST and the
University of Colorado). Cornell and Wieman are recognized for
their being the first to achieve a Bose-Einstein condensate (BEC) in
neutral atoms (Science, 14 July 1995; see Physics News Update 233).
Ketterle soon thereafter produced a larger BEC and has made
extensive study of BEC properties. The BEC phenomenon, foreseen
by Satyendra Bose and Albert Einstein in the 1920s, can come about
when atoms are chilled to very low temperatures. Quantum theory
holds that the wavelike nature of atoms allows them to spread out and
even overlap. Indeed at a high enough density and a low enough
temperature (billionths of degrees above absolute zero) the atoms
can, like the photons in a laser, enter into a common quantum state
with a common energy. In other words, the atoms are all coordinated
(coherent) with each other and constitute a single "super atom." BEC
was possible experimentally when in a magnetoptic trap (MOT) a
combination of laser cooling (a web of laser beams hitting the atoms
from many directions) and evaporative cooling (a web of magnetic
fields encourage the warmer atoms to depart, leaving the cooler
atoms to coalesce in the trap) brought about unprecedentedly low
temperatures. BEC is still largely restricted to fundamental research
in physics labs, but numerous potential applications beckon, such as
the use of BEC beams ("atom lasers") for doing high-resolution
lithography for microchips, interferometry (navigation, gravity wave
detectors, etc.), high-precision clocks, and "atomtronics" (atoms sent
around a microchip or down hollow fibers).
Physics News Update (http://www.aip.org/physnews/update) has
covered BEC research extensively. Examples include BEC as a
superfluid (Update 449), rudimentary atom laser (305), amplifying
atom waves (465), all-optical BECs (545), switching BEC
interactions from negative to positive (producing miniature
"supernovas," Update 530), BEC on a microchip (559), BEC as an
immiscible liquid (402), hydrogen BEC (382), lithium BEC (237),
helium BEC (532), tunable chemistry (362), sound waves in BEC
(319), slowed light in a BEC (472), quantum evaporation (356), and
continuous atom laser beam (422). (Background: Wieman and
Cornell, Scientific American, March 1998.)
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acoustics astronomy computers einstein gravity lasers low temperature quantum theory superfluids elements education optical fibres |
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QUANTUM FINGERPRINTING. Imagine two offices, located
halfway around the world, and their headquarters wants to make
sure that they each have the identical copy of a database. Imagine
further that the databases are huge--10^20 bits each. They could
transmit the database to the headquarters, and the headquarters
could compare them. But transmitting 10^20 bits--equal to about
11 billion gigabytes would take an enormous amount of time.
There is a method in which they only need to send 10^10 bits--a
little over a gigabyte--and the headquarters still gets enough
information to determine that they have the exact same database.
This method is called "classical fingerprinting." The idea is that
each office independently, without communicating to each other,
generates a distinctive number, called a fingerprint, by performing
a calculation involving the entire database and locally generated
random numbers, called keys. The result of the calculation-a
fingerprint of 10^10 bits--is then sent to the headquarters. Now, a
Dutch-Canadian team (Harry Buhrman, CWI/University of
Amsterdam, 011-31-20-5924076, buhrman@cwi.nl) has suggested
a "quantum fingerprinting" scheme which would involve an
exponentially smaller transmission of information to do the same
job. For the 10^20 bit database, each office would only have to
transmit a fingerprint of about 70 "quantum bits" (qubits), which
could be, for example, specially prepared photons. Such photons
could contain the result of a computation between the database and
many different random keys simultaneously, rather than a single
random key. The researchers say that one could demonstrate this
new fingerprinting technique with quantum computers not much
more complex than the ones that exist today. Buhrman estimates
that quantum fingerprinting becomes more efficient than classical
fingerprinting in a quantum computer with 5 to 10 qubits. (H.
Buhrman; R. Cleve; J. Watrous; R. de Wolf, Physical Review
Letters, 15 Oct. 2001; full text at www.aip.org/physnews/select)
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computers quantum theory |
| A follow-up to one of the articles in this update appeared in: Update 561 | |
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