Quantum optics physicists win Nobel Prize

0 Comments | Deseret News (Salt Lake City), Oct 5, 2005 | by Kenneth Chang New York Times News Service

A scientist who worked out a theory describing the behavior of light using quantum mechanics and two scientists who used that knowledge to develop a powerful laser technique for identifying atoms and molecules were awarded the Nobel Prize in Physics on Tuesday, the Royal Swedish Academy of Sciences announced.

Half of the prize and half of $1.3 million prize money goes to Roy J. Glauber, 80, a professor of physics at Harvard, for calculations that laid the foundation for quantum optics.

John L. Hall, 71, a physicist at the National Institute of Standards and Technology in Boulder and at the University of Colorado, and Theodor W. Haensch, 63, a physicist at the Max Planck Institute of Quantum Optics in Garching, Germany, and a professor of physics at the Ludwig Maximilians University in Munich, share the other half of this year's prize for later work that uses ultrashort laser pulses to make precise measurements.

One of the central, baffling properties of quantum mechanics, the strange rules that govern subatomic particles, is that light sometimes acts like waves, almost like ripples in a pond, while at other times, it appears to consist of discrete particles known as photons.

Physicists as far back as Einstein established the existence of photons and developed theories to describe how one or a few photons bounced off matter, almost like billiard balls. But they lacked a good understanding of the collective behavior of many, many photons.

"The mathematics can become infinitely complicated," Glauber said. Further, he added, "it wasn't clear there was a need to take that into account explicitly in experiments."

As a result, physicists continued to use the equations of classical optics from the 19th century, which successfully described most phenomena involving light.

"It occurred to me around the early '60s that that was not going to be true in the long run," Glauber said, "and one had better develop the quantum theory to the fullest extent mathematically possible."

Glauber was initially intrigued by astronomical observations of the star Sirius by Robert Hanbury Brown and Richard Q. Twiss, who counted photons from Sirius using two identical detectors 20 feet apart. The expectation was that photons from Sirius would arrive randomly like raindrops, but instead, the scientists detected a pattern in the arrival of photons in the two detectors.

Glauber and others, including E.C. George Sudarshan, a professor at the University of Texas, worked to explain the observations through quantum mechanics. Glauber's theory, published in 1963, showed how the patterns of bunching, called coherence, could emerge during the photons' travel to Earth.

H. Jeff Kimble, a professor of physics at the California Institute of Technology, said Glauber took the existing quantum theory of electromagnetism and cast it "in a form where it's clear how to apply it to these other phenomena."

The work of Glauber helped explain the differences between the diffuse light of a light bulb and the intense beam of a laser, which was invented about that same time. His theory is also fundamental to using light in developing quantum computers and quantum cryptography.

"It was Glauber's theory which was the basis for all of that," said Daniel Kleppner, a professor of physics at the Massachusetts Institute of Technology, "You didn't need Glauber's theory to invent the laser, but you needed Glauber's theory to understand its properties."

Decades later, Hall and Haensch built upon that work. Hall helped lead efforts to use lasers to measure the speed of light precisely. As a result, in 1983, the speed of light in a vacuum was defined to be exactly 299,792,458 meters per second, and a meter was defined as the distance that light travels in one-299,792,458th of a second.

For the Nobel Prize, the academy cited work by Hall and Haensch that led to a technique that uses short pulses of laser light as a sort of ruler to measure the color, or frequency, of light, that is accurate to one part in one-quadrillion.

Haensch first proposed the technique, called the optical frequency comb, in the late 1970s.

On Tuesday, Hall said that when he first saw Haensch's paper, he thought it was "genius, prophetic or absolutely absurd" -- and at the time, his opinion leaned more to the latter. "I didn't see any way to make that happen," Hall said.

The technique required a laser to shoot ultrashort pulses of light at a steady wavelength, and as the years passed, the laboratories of Hall and Haensch, at times collaborating, at times competing, made progress. Hall and his collaborators solved the final problems to applying the comb technique about five years ago.

The colors of light emitted or absorbed by atoms and molecules in substances can enable scientists to identify the composition of the materials, and the technique may help them create more accurate clocks and experiments that can determine if fundamental properties of the universe change over time.

The precise control of light beams, through lasers with very sharp colors, could even provide better entertainment.