Physics News Update no. 571
This report comments on special relativity, slowing and storing light in a solid, and the workings of a sonic crystal.
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The American Institute of Physics Bulletin of Physics News
Number 571 January 2, 2002
Published by the American Insitute of Physics.
A NEW LIMIT ON THE OVERALL VALIDITY OF SPECIAL
RELATIVITY has been established by a group of physicists the University of Konstanz (Germany) quantum optics lab in collaboration with the University of Düsseldorf. In a sense this is the highest accuracy overall test of special relativity, a pillar of modern physics. One of the principles of relativity theory is that the velocity of light, c, will be the same as measured by all observers. Thus, for example, an observer on a train moving very quickly toward a signal lamp will record the same light speed as an observer at rest next to the train tracks; the velocity of the train does not in any make the apparent light speed any greater. In a Michelson-Morley-type experiment (MM) the universality of observed light speed is demonstrated by comparing light beams moving in different directions.
In another class of experiments, called Kennedy-Thorndike tests (KT), one tests that c does not depend on the velocity of the laboratory. Since present MM precision is higher than the best KT precision, the Konstanz researchers aimed for a better KT test as a way of confirming, to a new level of accuracy, that c is independent of both the speed and direction of the lab. Basically they keep watch over a set of standing light waves in a chilled cavity over a 190 day period, during which the Earth traces out more than one half of its orbit around the sun, altering the velocity of the "lab" by an amount equal to 60 km/sec. If c were to vary with lab speed, then the standing waves (constantly compared to a highly stable atomic clock) would fall out of tune with the cavity; the cavity itself, made of sapphire, has very little thermal expansion at a temperature of 4 K, and could be counted upon to keep its shape.
In this way the stability of the resonance frequency translated into a three-fold improvement in accuracy over past KT experiments. A 100-fold improvement in the near future is anticipated. (Achim Peters, 49-7531-88-3823, achim.peters@uni-konstanz.de; Holger Mueller, holger.mueller@uni-konstanz.de) (Braxmaier et al., Physical Review Letters, 7 January 2002; see also this link)
SLOWING AND STORING LIGHT IN A SOLID. When light encounters a medium in which the index of refraction changes dramatically with wavelength, the group velocity of light, the speed at which the wave pulse propagates, can be considerably lowered, even to zero. The energy and information in the original light beam can be stored, without any heating, in the form of a wave of excitations in the spins of the atoms in the medium. Earlier this year two different experiments at Harvard stopped and stored light in a vapor sample (Update 521). Now the feat has been carried out in a solid material in an experiment carried out at MIT and at the Air Force Research Laboratory in Hanscom, Massachusetts. This is a nice advance since in general information processing is carried out in solid-state integrated devices. The medium used, a yttrium-silicate crystal doped with atoms of the rare earth praseodymium, is already commonly used as a medium for high-density optical data storage. The researchers (contact Philip Hemmer, 781-377-5170, philip.hemmer@hanscom.af.mil) foresee many applications for slow or stopped light in a solid, in areas such as quantum computing, ultra-sensitive magnetometry, and acousto-optics (if light is slowed to subsonic speeds, strong coupling between light and sound waves becomes possible). (Turukhin et al., Physical Review Letters, 14 January 2001)
A SONIC CRYSTAL is to sound waves in air what a photonic crystal is to light waves or a semiconductor is to electrons it permits the passage of waves at some energies but not others. Scientists in Spain (contact Francisco Meseguer Rico, fmese@fis.upv.es, 349-6387-9841; Jose Sanchez Dehesa, jsdehesa@upvnet.upv.es) are the first to use a sonic crystal, an arrangement made of aluminum rods, as an acoustic lens for focusing sound waves at audible frequencies.
They also create thereby an interferometer which, like its lightwave counterpart, causes two wavetrains of soundwaves to interfere with each other in a characteristic pattern. (Cervera et al., Physical Review Letters, 14 January 2002)
Number 571 January 2, 2002
Published by the American Insitute of Physics.
A NEW LIMIT ON THE OVERALL VALIDITY OF SPECIAL
RELATIVITY has been established by a group of physicists the University of Konstanz (Germany) quantum optics lab in collaboration with the University of Düsseldorf. In a sense this is the highest accuracy overall test of special relativity, a pillar of modern physics. One of the principles of relativity theory is that the velocity of light, c, will be the same as measured by all observers. Thus, for example, an observer on a train moving very quickly toward a signal lamp will record the same light speed as an observer at rest next to the train tracks; the velocity of the train does not in any make the apparent light speed any greater. In a Michelson-Morley-type experiment (MM) the universality of observed light speed is demonstrated by comparing light beams moving in different directions.
In another class of experiments, called Kennedy-Thorndike tests (KT), one tests that c does not depend on the velocity of the laboratory. Since present MM precision is higher than the best KT precision, the Konstanz researchers aimed for a better KT test as a way of confirming, to a new level of accuracy, that c is independent of both the speed and direction of the lab. Basically they keep watch over a set of standing light waves in a chilled cavity over a 190 day period, during which the Earth traces out more than one half of its orbit around the sun, altering the velocity of the "lab" by an amount equal to 60 km/sec. If c were to vary with lab speed, then the standing waves (constantly compared to a highly stable atomic clock) would fall out of tune with the cavity; the cavity itself, made of sapphire, has very little thermal expansion at a temperature of 4 K, and could be counted upon to keep its shape.
In this way the stability of the resonance frequency translated into a three-fold improvement in accuracy over past KT experiments. A 100-fold improvement in the near future is anticipated. (Achim Peters, 49-7531-88-3823, achim.peters@uni-konstanz.de; Holger Mueller, holger.mueller@uni-konstanz.de) (Braxmaier et al., Physical Review Letters, 7 January 2002; see also this link)
SLOWING AND STORING LIGHT IN A SOLID. When light encounters a medium in which the index of refraction changes dramatically with wavelength, the group velocity of light, the speed at which the wave pulse propagates, can be considerably lowered, even to zero. The energy and information in the original light beam can be stored, without any heating, in the form of a wave of excitations in the spins of the atoms in the medium. Earlier this year two different experiments at Harvard stopped and stored light in a vapor sample (Update 521). Now the feat has been carried out in a solid material in an experiment carried out at MIT and at the Air Force Research Laboratory in Hanscom, Massachusetts. This is a nice advance since in general information processing is carried out in solid-state integrated devices. The medium used, a yttrium-silicate crystal doped with atoms of the rare earth praseodymium, is already commonly used as a medium for high-density optical data storage. The researchers (contact Philip Hemmer, 781-377-5170, philip.hemmer@hanscom.af.mil) foresee many applications for slow or stopped light in a solid, in areas such as quantum computing, ultra-sensitive magnetometry, and acousto-optics (if light is slowed to subsonic speeds, strong coupling between light and sound waves becomes possible). (Turukhin et al., Physical Review Letters, 14 January 2001)
A SONIC CRYSTAL is to sound waves in air what a photonic crystal is to light waves or a semiconductor is to electrons it permits the passage of waves at some energies but not others. Scientists in Spain (contact Francisco Meseguer Rico, fmese@fis.upv.es, 349-6387-9841; Jose Sanchez Dehesa, jsdehesa@upvnet.upv.es) are the first to use a sonic crystal, an arrangement made of aluminum rods, as an acoustic lens for focusing sound waves at audible frequencies.
 Sonic Crystal http://www.aip.org/mgr/png |
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