update.557 (fwd)

[Jim Choate]

---------- Forwarded message ----------
Date: Thu, 20 Sep 2001 13:34:25 -0400 (EDT)
From: AIP listserver <physnews at aip.org>
To: physnews-mailing at aip.org
Subject: update.557


PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 557  September 20, 2001   by Phillip F. Schewe, Ben Stein,
and James Riordon

THE GREENING OF NORTH LATITUDES.  A new study shows
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AN ANOMALOUS ACOUSTOELECTRIC EFFECT has been
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MULTIPLAYER QUANTUM GAMES.  Played with atoms and
photons rather than dice and coins, quantum games are contests
whose outcomes are governed by the unusual logic of the
submicroscopic world.   The basic token in a quantum game is a
"qubit," a bit of data which is stored in an object such as an atomic
nucleus.  While a classical coin can only be heads (data value 0) or
tails (data value 1), a qubit can effectively be both heads (0) and
tails (1) at the same time, since the nucleus can be in a
combination or superposition of spin-up (0) and spin-down (1). 
What's more, one can interlink or "entangle" qubits held by
separate players so that manipulating one qubit strongly affects the
others.  More than a diversion, playing quantum games can reveal
new information-processing tasks (possibly even certain types of
financial transactions) that quantum computers could perform
more efficiently than classical computers.  Towards these ends,
theorists have been taking traditional games, adapting them for the
quantum realm, and checking if new or better strategies emerge for
winning.  While past quantum games have focused on two players
(Update 411), Oxford researchers (Patrick Hayden,
Patrick.hayden at qubit.org) have now identified multiplayer games
in which the player's optimal strategy differs from that of the
classical version of the game.  The researchers discovered unique
strategies in a three-player quantum version of the Dilemma game,
in which three partners engaged in a venture (such as getting the
best seats at a concert) each decide whether or not to betray the
others in efforts to maximize personal gain.  In the quantum
version, the qubits are entangled, then each person uses his qubit to
choose between the following strategies: try for good seat (0),
settle for poor seat (1) or some superposition of the two.  
Entanglement actually destroys the incentive for a player to
contradict and thereby betray his opponents and it removes the
classical dilemma entirely. Although quantum games are mostly
played on paper at this point, a Chinese group has just reported the
experimental realization of a quantum Prisoner's Dilemma (Los
Alamos preprint quant-ph/0104087).  (Benjamin and Hayden,
Physical Review A, September 2001)