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From physnews@aip.org Mon Jun 3 17:03:16 1996 Date: Mon, 3 Jun 96 14:06:02 EDT From: physnews@aip.org (AIP listserver) Message-Id: <9606031806.AA07182@aip.org> To: physnews-mailing@aip.org Subject: update 273
PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 273 May 31, 1996 by Phillip F. Schewe and Ben Stein SCHRODINGER'S CAT-ION: Physicists at NIST (Christopher Monroe, 303-497-7415) have experimentally demonstrated the principles of the famous Schrodinger's cat thought experiment with a single beryllium ion. In a 1935 paper, physicist Erwin Schrodinger proposed the cat paradox: put a cat inside a box, add a container of poison gas which is activated by the decay of a radioactive atom, and close the box. Since the radioactive atom obeys the rules of quantum mechanics and since therefore its state is indeterminate until measured by an outside observer, opening the box and observing the atom (a microscopic quantum system) instantly determines the status of the cat (a decidedly macroscopic, non-quantum concept). The feline is neither alive nor dead until the radioactive atom is measured by an observer. Although this thought experiment is impossible to carry out for a number of reasons, including the fact that the quantum properties of a system tend to wash out in an object made of many atoms and molecules such as a cat, the NIST physicists have demonstrated the basic principles using a single beryllium ion. The researchers trap the ion with nonuniform electric fields and cool it to a near standstill. Laser pulses then cause the ion to oscillate as a combination of wavepackets representing two different electronic states. Additional laser pulses push apart the two wavepackets to separations of as much as 80 nanometers, a mesocopic-size scale far bigger than the normal spatial extent of the ion. So in this version of Schrodinger's cat, the ion's electronic state (a quantum property) is linked to (or "entangled" with) a mesocopic-scale position (a non-quantum property). By applying subsequent pulses that bring together the wavepackets, the researchers detected interference patterns which provided evidence of the original separation. Measurements of Schrodinger cat's states can provide information on how quantum properties wane with the amount of physical separation between quantum states. (C. Monroe et al., Science, 24 May 1996.) SUPERCONDUCTING TUNNEL JUNCTIONS (STJ), under development as efficient detectors of x rays, can now also be used as single-photon detectors at visible wavelengths. In this regard they will be welcomed by astronomers who increasingly record incoming light with charge-coupled device (CCD) arrays. In contrast to the silicon-based CCDs, which are insensitive to a photon's energy (one photon engenders one electron in the detector), the niobium-based STJ's do discriminate as to energy (one photon, depending on its energy, can generate thousands of electrons). Determining a photon's energy would allow astronomers to forego filters, which lower the detector's overall efficiency. A STJ device developed by an Oxford-Cambridge-European Space Agency (Netherlands) collaboration can detect light in the wavelength range 200-500 nm with a spectral resolution of 45 nm (this should improve to 20 nm or better). The STJ can also determine the photon's time of arrival at the millisecond level, a property the would be handy for studying fast astronomical processes such as pulsars. (A. Peacock et al., Nature, 9 May 1996.) PHYSICS BACHELOR'S DEGREES. Here are some highlights from a new AIP report on 1994 degree recipients in the U.S.---the annual number of degrees continues to decline slightly; more fresh graduates are looking for jobs rather than heading for graduate school; for those going on in their studies 89% receive financial support; women constitute 17% of the degree recipients; median starting salary was $27,000. (Patrick Mulvey, 301-209-3076.)