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.)
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