freezing light
Here's an atricle on it from
http://www.afrlhorizons.com/Briefs/Jun02/OSR0201.html
A scientist's breakthrough could lead to the manufacture of quantum computers.
AFRL's Air Force Office of Scientific Research, Arlington VA
A researcher's achievement would have surprised even Dr. Albert Einstein. Dr. Lene Hau, a Gordon McKay Professor of Applied Physics and professor of physics at Harvard University in Cambridge, Massachusetts, and her colleagues made light stand still. "We slowed light to a complete stop and froze it in place for up to several 1,000ths of a second, an eternity to a light beam," said Hau in a U.S. News & World Report interview.
As of yet, no scientist has disproven Einstein's theory that a signal light cannot travel faster than 186,282 miles per second, but Einstein never said it couldn't go slower. In a vacuum, nothing travels faster than light; however, all ordinary transparent media or materials slow down light. Water slows light to about 75% of its speed in a vacuum. A non-transparent object, like a brick wall, can stop a beam of light, but it destroys the information that can be coded in the light beam in the process.
In 1999, Dr. Hau slowed a light pulse down 20 million-fold to a leisurely 38 miles per hour. She and her team first created a small cigar-shaped cloud of sodium atoms trapped in a magnetic field and cooled to temperatures colder than those found in space. They illuminated the cloud with a carefully tuned laser beam that altered the optical properties of the cold atom cloud dramatically (see Figure 1). The team subsequently sent another light pulse into the cloud and then slowed this pulse, while at the same time compressing it spatially from a length of one mile in free space to only 0.002 in. within the cloud.
The key, Dr. Hau noted, was to chill the atoms to a temperature within a millionth to a billionth of a degree of -459.7?F, referred to as absolute zero. Absolute zero is the temperature where atoms have the lowest amount of energy and any activity nearly ceases. The sodium atoms were cooled by a combination of laser beams, magnetic fields, and radio waves.
In 2000, the Air Force Office of Scientific Research (AFOSR) began sponsoring Dr. Hau's research. Later that year, Dr. Hau used a similar technique to completely stop the pulses. A laser beam converted the frozen pulse back into a moving light pulse, but significantly, with all of its original properties. This allowed researchers to control a light pulse by capturing and storing it, thus enabling them to release it at will. Dr. Hau and her colleagues "... believe that this system could be used for quantum information transfer, ... and with use of controlled atom-atom interactions, quantum information processing may be possible during the storage time."1
Under AFOSR sponsorship, Dr. Hau and her group are currently continuing their research into optical information storage in an atomic medium using halted light pulses. One possible Air Force application for this breakthrough could be a new generation of computers called quantum computers. Quantum superpositions of ones and zeros, called qubits, would replace the usual definite ones and zeros used in binary coding. If manufactured, these computers could solve problems completely inaccessible to today's computers. An intriguing aspect of this research to quantum computer designers is that when light is stopped, all of its original characteristics are transferred to the cloud's atoms. When the light is unfrozen, the information is then transferred back to the light from the atoms. This link, photon-to-atom, could become the quantum circuits of tomorrow's computers.
Nonlinear optics, with applications from telecommunications to imaging, is another field of research to benefit from this breakthrough. Usually, researchers need exceptionally powerful beams to achieve nonlinear optical effects, but using slow light techniques can achieve the same phenomena with only a small number of photons. This effect could benefit the design of ultrasensitive optical switches.
Other practical Air Force uses of this light-stopping research include new ways to communicate solely by light and through coding methods. This would protect both military and personal information, and control optical information storage.
