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Number 411, January 19, 1999 by Phillip F. Schewe and Ben Stein
QUANTUM GAMES. Star Trek's Captain Picard (fictional commander of the USS Enterprise) and Q (his mischievous, all-powerful adversary) are beamed onto the pages of Physical Review Letters for the first time to engage in a hypothetical contest that represents the extension of game theory to the quantum world. With these characters, physicist David Meyer of the math department (Project in Geometry and Physics) at UC-San Diego (619- 534-5524; dmeyer@chonji.ucsd.edu) illustrates how playing nanoscopic versions of familiar games with atoms (or any other object which obeys the peculiar rules of quantum mechanics) may reveal new information-processing tasks (beyond already known ones) that quantum computers would perform more efficiently than classical computers. In Meyer's scenario, Q promises Picard that he will help get the Enterprise out of its latest emergency if Picard wins a game. Specifically, the contest amounts to a quantum version of a penny- flipping game, in which an atomic nucleus with "spin-up" and "spin-down" states takes the place of the familiar zinc coin with heads and tails. Through this game, Meyer shows that players like Q who exploit the unique properties of quantum-mechanical objects (such as the ability to put it in a simultaneous combination or "superposition" of two states) enjoy a distinct advantage over those who (like Picard) just treat the objects like everyday items such as balls or coins (which can only be in one state or the other). Through his use of superpositions, Q manipulates the nucleus in such a way that ensures he always wins, even though the chances of winning the classical version of the game are only 50-50. Such a contest, Meyer points out, can be easily demonstrated with the rudimentary quantum computers that now exist (Updates 250, 310, 367), and may provide insights on such things as quantum-error correction (Update 388). (Meyer, Physical Review Letters, 1 February 1999; as usual, journalists can obtain the article from AIP Public Information.)
X RAYS IN, GAMMA RAYS OUT. A laser is a machine for pumping energy (electrical, light, chemical, etc.) into a medium (liquid, gas, solid, etc.) whose atoms subsequently relax in a concerted way, producing coherent light. One of the obstacles to creating an x-ray or gamma laser is the inability to pack enough energy into the medium and have it sit there long enough until it can be extracted under the right circumstances. One candidate medium for the job is isomeric hafnium. In nuclear physics isomers are nuclei that have the same number of neutrons and protons but differ in that for one nucleus one or more nucleons (protons or neutrons) are placed in an excited state. Physicists at the University of Texas at Dallas (Carl Collins, 972-883-2864, cbc@utdallas.edu) and their colleagues in Russia, Romania, Ukraine, and the US begin with a sample (prepared at Los Alamos) of a metastable (31-year lifetime) isomer of Hf-178 with 4 participating nucleons, possessing a stored energy of 2.5 MeV. Then, like a transistor triggered by the merest of gate signals, the isomer material can, with the input of some x rays (amounting to only 1.6% of the output energy), produce induced gamma emission (IGE); thus x ray energy is stockpiled in the Hf and later extracted at higher gamma-ray energy. The emitted rays are not coherent, however, so this is not yet an example of gamma lasing. IGE research also has astrophysical implications since isomer states are expected to behave differently in gamma-intense environments such as supernovas. (C.B. Collins et al., Physical Review Letters, 25 January 1999; see http://www.utdallas.edu/research/quantum.)
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