From: John K Clark (johnkc@well.com)
Date: Thu Apr 16 1998 - 09:03:54 MDT
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- From PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 367 April 15, 1998 by Phillip F. Schewe and Ben Stein
A SEARCH ENGINE THAT EMPLOYS QUANTUM WEIRDNESS
has been experimentally demonstrated, allowing researchers
to successfully find one of four possible pieces of data
in a single computational step, rather than the 2.25 steps it takes
traditional computers on average. Executing a quantum search
algorithm proposed by Bell Labs physicist Lov Grover (Physical
Review Letters, 14 July 1997; Physics Today, October 1997),
an IBM-MIT-Berkeley team (Isaac Chuang, IBM-Almaden, 408-927-8245)
employed an "NMR" quantum computer (Update 310), a device
in which the binary digits 0 and 1 are represented by
an atomic nucleus respectively aligned with and opposed to an
external magnetic field. Starting with a solution of liquid
chloroform molecules, and using radio pulses to manipulate the
inner magnets of the carbon and hydrogen nucleus in each
molecule, the researchers first put each carbon and hydrogen
nucleus into a combination or "superposition" of 0 and 1 states,
for a total of four possibilities in each molecule. Because quantum
systems can be in many states at the same time, each molecule
would then respond for all 4 possible states at once. Then they fired
one of four possible sequences of radio pulses. By measuring the
response of the collection of molecules, the researchers were then
able to deduce the pulse sequence in a single step. Equivalent to
finding one of 4 items in a database, this is the first experimental
demonstration of a quantum computation requiring fewer steps than on a
classical computer. (Chuang et al., Phys. Rev. Lett., 13 April 1998.)
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