From top: Roy J. Glauber, Theodor W. Haensch and John L. Hall

A scientist who worked out a theory describing the behaviour 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 yesterday, the Royal Swedish Academy of Sciences announced.

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. H?nsch, 63, a physicist at the Max Planck Institute of Quantum Optics in Garching, Germany, and a physics professor at the Ludwig Maximilians University in Munich, share the other half of the 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 Albert 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 behaviour of many, many photons. “The mathematics can become infinitely complicated,” Glauber said.

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 60’s 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 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.

Hall and H?nsch built upon Glauber’s 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 H?nsch that led to a technique that uses short pulses of laser light as a sort of ruler to measure the colour, or frequency, of light, accurate to one part in one-quadrillion. H?nsch first proposed the technique, called the optical frequency comb, in the late 1970’s.

(Kenneth Chang / NYTNS)