Re: New Light-Based Computer Runs At Quantum Speeds

From: John Clark (
Date: Sat May 19 2001 - 07:48:20 MDT

The American Institute of Physics Bulletin of Physics News
Number 539 May 15, 2001 by Phillip F. Schewe, Ben Stein, and
James Riordon

COMPUTING WITH WAVES. Conventional computers do their
jobs by using electrons as billiard-ball like particles to move
around circuits and carry out the desired tasks. At last week's
CLEO/QELS lasers/optics conference in Baltimore, a University
of Rochester group (Ian Walmsley, 716-275-0312, presented a simple optical system
that performs a database search of 50 items in a way that cannot be
duplicated in any particle-powered computer. To do the search,
the researchers use wave interference, the patterns that are created
when two waves, such as light waves, combine. While their
demonstration is not any more efficient than traditional database
searches, it is the largest search performed with wave interference.
It is a follow-up to a similar demonstration in an atom (Ahn et al.,
Science, 21 January 2000) and expands possibilities for "wave
computing" which would be intermediate in power between
classical computing and quantum computing. In addition, the
Rochester group uses light, which is much easier to prepare and
transport than atoms. In their demonstration, the researchers
produce a single pulse of light carrying a spectrum of different
colors, each containing a different bit of information. They split
the pulse into two identical pulses each with half the intensity. One
travels to an "Oracle," an optical element (an acousto-optic
modulator) which for certain colors shifts their phase, the relative
position of the peaks of the wave compared to other colors. Then
they combine the Oracle pulse with the other, untreated pulse at a
beamsplitter, which produces two output beams, each going in
different direction. Only the components of the beam which have
their phases changed travel toward a spectrometer and detector,
enabling the researchers to read out the information and determine
the location of the desired item in the database. (Paper QWB3;

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