University of Rochester

500 Scientists to Share Findings on Nature of Light

May 25, 1995

"All these 50 years of conscious brooding have brought me no nearer to the answer to the question, "What are light quanta?" Nowadays every Tom, Dick and Harry thinks he knows it, but he is mistaken." -- Albert Einstein in 1951.

After studying light and its most fundamental particles, photons (or light quanta), for more than half a century, even Albert Einstein had difficulty understanding and explaining the subject. So it should come as no surprise that, nearly 45 years later, hundreds of scientists around the world are still seeking answers to the most basic questions about the nature of light and photons.

More than 500 of these scientists from five continents will descend upon the University of Rochester for five days next month for the biggest conference of the decade on coherence and quantum optics. The Seventh Rochester Conference on Coherence and Quantum Optics, long considered the world's premier conference in the field, will be June 7-10 on campus.

Scientists will discuss the nature of light and the many surprising ways in which light interacts with matter. Among the topics: cooling atoms almost to a standstill; exploring the boundary between classical and quantum physics; results from new types of lasers, including tiny one-atom micro-lasers; better ways to generate, clean and control laser beams; and subtle ways in which energy can be redistributed among different wavelengths as light propagates.

The conference will include tutorials by top names in the field, including Claude Cohen-Tannoudji of Paris, and German physicists Herbert Walther and Wolfgang Schleich. More than 25 scientists will give invited lectures, and more than 250 will present their work in poster sessions and in rapid 1.5-minute presentations.

The conference, held at the University every five or six years since 1960, will take place along with a conference on Nonlinear Dynamics in Optical Systems and a Symposium on Spectral Effects in Collective Phenomena.

At about the same time that the first conference took place, the first laser was invented, and since then the conferences have proven to be a record of advances that cover a wide range of optical physics, including lasers, optical communications, and many kinds of basic phenomena involving light and atoms. Even so, many scientists who will attend the meeting are still asking fundamental questions in areas such as quantum mechanics, whose predictions even Einstein had trouble accepting.

The conference is sponsored by the American Physical Society, the Optical Society of America, the University, and the International Union of Pure and Applied Physics. tr SELECTED TOPICS AT THE SEVENTH ROCHESTER CONFERENCE ON COHERENCE AND QUANTUM OPTICS

Lasing without population inversion -- a new type of laser

Scientists will discuss a newly discovered process, "lasing without population inversion," that is unexpected, given the laws of physics that govern lasers.

In a traditional laser, atoms are pumped full of light and then release that light in sync. These new types of lasers appear to work very differently from conventional lasers; the atoms do not seem to store as much light as previously thought before lasing. The process would have implications for the construction of X-ray or ultraviolet lasers. Presenters include Marlan Scully of Texas A&M and Olga Kocharovskaya of the former Soviet Union.

Laser cooling -- coldest spot in the universe

Several scientists will present their latest results on laser cooling, where laser beams are used to bombard an atom to a near standstill, cooling it to just a fraction of a degree within absolute zero, nearly the coldest temperature possible in the universe. At these temperatures, atoms begin exhibiting strange interference effects, acting less like discrete particles and more like waves. For instance, physicists have shown that a single ultra-cold atom can travel down separate paths and interfere with itself. Among the applications being investigated: compact super-precise clocks, and "optical tweezers" that scientists can use to isolate individual atoms and even living cells.

Presenters in this area include Claude Cohen-Tannoudji of Paris, Nicholas Bigelow of Rochester, and David Pritchard of MIT.

Classical vs. quantum mechanics

For much of the early half of this century, some of the greatest physicists of all time -- such as Bohr, Einstein, and Born -- argued over the true meaning of the laws of quantum mechanics. Classical physics rules the world that most of us are familiar with, but in the world of the atom, quantum mechanics is necessary to explain the observations scientists routinely see in the laboratory. The domain where classical physics breaks down, and where somewhat larger objects demonstrate bizarre quantum behavior, has long intrigued physicists.

Now, advances in short-pulse lasers have made possible the creation of huge atoms, sometimes one micron in diameter, that display the "classical" behavior of an electron orbiting a nucleus for a short period of time -- systems as small as atoms are behaving "classically." Meanwhile, engineers are creating transistors and other structures smaller than a millionth of a meter, a domain where quantum laws reign. Such experiments are allowing them to test some of the tenets of quantum mechanics.

A "CT scan" of a molecule

Most people are familiar with computerized tomography (CT) scans used by physicians to take a series of images of a patient's body and then use computers to reconstruct a three- dimensional image of the body.

Now, by taking advantage of recent results in quantum optics, scientists are using very similar techniques to take new, more complete 3D images of molecules and even photons. They do this by reconstructing the interference pattern created by a single photon or molecule. The techniques give scientists the wave function of a system, a key to fully understanding the behavior of a system.

Atom optics

One rapidly growing area is atom optics, where scientists use atoms instead of photons to examine objects. Scientists are looking at atom optics to design more sensitive ways to detect gravity, or even to use atoms to help make computers chips. Scientists think that atom microscopes, atom interferometers, and even atom lasers are possible.

Shifting frequency of light

Many laboratories are demonstrating a mechanism discovered not long ago at the University of Rochester to shift the spectrum of light as it travels through space. Potential applications of this effect, known as the "Wolf Effect," include more rapid astronomical measurements and new ways to encode signals. Most of the Symposium on Spectral Effects in Collective Phenomena is devoted to this topic.

Transparency -- using one laser beam to "fix" another

Conference participants will discuss new ways to use one laser beam to control another one. Using one beam to modulate or even improve another could have applications in optical computing, for instance, or in telecommunications or satellite communications, where laser beams must travel long distances through the atmosphere. Presenters of this work on transparency include Joe Eberly at Rochester, Klaus Bergmann of Germany, and Steve Harris at Stanford.