Physicists create atom-cavity microscope, track single atoms bound in orbit with single photons

PASADENA—In a promising development with applications to science at the single-atom level, physicists have constructed an "atom-cavity microscope" that tracks the motion of individual atoms.

California Institute of Technology physics professor H. Jeff Kimble, his Caltech colleagues, and collaborators from New Zealand report in the February 25 issue of Science that they have succeeded in monitoring the motion of individual cesium atoms bound in orbit by single photons inside a high-quality optical resonator. The atom is trapped in orbit by a weak light field, and the same light field can be used to observe the atom's motion within the cavity.

This advance is an important development toward the eventual realization of quantum technologies, which would enable quantum computation and communication.

The stage for this microscopic dance is the optical cavity, a pair of highly reflective mirrors that face each other only 10 microns (0.0004 inches) apart. The mirrors are so reflective that a photon, the fundamental quantum of light, enters the cavity and bounces back and forth between the mirrors hundreds of thousands of times before it escapes again through one of the mirrors.

In this way a single photon confined in the cavity builds up an electric field strong enough to influence the motion of an atom and even to bind the atom in orbit within the cavity.

Collaborating theorists A. Scott Parkins and Andrew Doherty in New Zealand first recognized the potential of this trapping technique, in which the atom and the cavity share a quantum of excitation.

"I like to think of it as an atom-cavity molecule," says Christina Hood, a Caltech graduate student and primary author of the paper. "In a molecule, two atoms give up their own electron orbits, their separate identities, to share electrons and form something qualitatively different. In the same sense, in our experiment the atom and the cavity field are bound together strongly by sharing a series of single photons."

How do the scientists actually "see" what is going on inside the tiny optical system? The Caltech group and others had already used similar cavities to sense single atoms whizzing through the cavity. To do this, they illuminate one mirror of the cavity and measure the light escaping from the opposite mirror. "The cavity is a resonator for light, like a half-filled soda bottle is for sound," says Theresa Lynn, a Caltech graduate student and coauthor of the paper. "What we do is similar to holding a tuning fork up to the bottle and listening to hear it resonate. You'll only hear a ring if the right amount of water is in the bottle."

In this case, amazingly, it's a single atom that plays the role of the water in the bottle, dramatically altering the resonance properties of the cavity by its presence or absence. By measuring the amount of light emerging from the cavity, the researchers can tell whether an atom is in the cavity or not.

The major step of the current work is that now they can determine precisely where the atom is located within the light field, creating "movies" of atomic motion in the space between the cavity mirrors. Examples of these movies can be viewed at the group's web site:

The movies show atoms trapped in the cavity as they orbit in a plane parallel to the cavity mirrors. The atoms have orbital periods of about 150 microseconds and are typically confined to within about 20 microns of the cavity's center axis.

The Kimble team was able to measure the atomic position to within about 2 microns in measurement times of about 10 microseconds. Continuous position measurements at this level of accuracy and speed allowed them to capture the orbital motions of the atoms.

"The interaction of the atom with the cavity field gives us advantages in two distinct ways," says Kimble. "On the one hand, it provides forces sufficient to trap the atom within the cavity at the level of single photons. On the other hand and more importantly, the strong interaction enables us to sense atomic motion in a fashion that has not been possible before," he says.

Both aspects are important to physicists who probe the limits of our ability to observe and to control the microscopic world, in which the rules and regulations are set by quantum mechanics. According to one basic rule of quantum mechanics, the Heisenberg uncertainty principle, any measurement performed on a system inherently disturbs the future evolution of that system. The principle presents a challenge to physicists who strive to control or "servo" individual quantum systems for use in quantum computation and other quantum technologies.

In collaboration with Caltech assistant professor Hideo Mabuchi, the Caltech team is pursuing extensions of the current research to implement real-time quantum feedback to control atomic motion within the cavity. The operating principles for such "quantum servos" are a topic of contemporary theoretical investigation at Caltech being pursued by Mabuchi, Doherty, and their colleagues.

The cavity as a powerful sensing tool by itself also presents possibilities outside the quantum realm. The same techniques that produce movies of orbiting atoms could be adapted to more general settings, such as to "watch" the dynamics of molecules engaged in chemical and biochemical reactions. Mabuchi is pursuing an independent effort along these lines to monitor single molecules engaged in important biological processes such as conformationally gated electron transfer.

Robert Tindol

New digital sky survey uncovers rare celestial objects

CHICAGO—A large new digital sky survey has been used by astronomers at the California Institute of Technology to discover distant quasars and other rare types of cosmic objects, including mysterious new objects of an unknown nature.

These results are being reported today at the meeting of the American Astronomical Society in Chicago.

The Caltech team, led by S. George Djorgovski, professor of astronomy, made the discoveries in an initial scientific exploration of the Digital Palomar Observatory Sky Survey (DPOSS). The survey, now nearing completion, covers the entire northern sky in three colors, and it is based on a photographic sky atlas (POSS-II) produced at Palomar Observatory.

The final product of the survey is the Palomar-Norris Sky Catalog, which will contain information on over 50 million galaxies and about two billion stars. It will be made available to the general astronomical community, beginning a few months from now.

When complete, DPOSS will contain several terabytes of information (a terabyte is 8 trillion bits, or about the amount of information contained in two million thick books). This is also over a thousand times larger than the amount of information in the entire human genome.

Comparable amounts of data are now being produced by several other digital sky surveys, including the Two-Micron All-Sky Survey (2MASS) in the infrared wavelengths, the forthcoming Sloan Digital Sky Survey (SDSS), which, like DPOSS, will cover the visible light part of the spectrum, and several NASA missions.

Other projects of a similar scope are now under way or are being planned.

"This is the dawn of the new era of information-rich astronomy," says Djorgovski. "This unprecedented amount of astronomical information will enable scientists and students everywhere, without access to large telescopes, to do first-rate observational astronomy."

Surveys like DPOSS can be used to study the universe in a systematic manner—for example, to probe the large-scale structure in the distribution of galaxies in some detail. But they can also be used to discover rare, or even previously unknown types of astronomical objects: the sheer numbers of detected sources make it possible to find objects that are one in a million or even one in a billion—an astronomer's needle in a digital haystack.

Caltech astronomers did exactly that in their initial scientific verification tests of the DPOSS data. The group used novel techniques to search the data for star-like objects with colors unlike those of the ordinary stars.

Some of these are types of objects they expected to find: for example, very distant quasars, seen at the time when the universe was less than 10 percent of its present age. Such quasars are valuable probes of the early universe and galaxy formation. The Caltech team has so far identified over 70 of them, more than the number found by all other groups in the world combined.

Perhaps even more interesting are surprises, unexpected findings of anomalous objects. The Caltech team has one such object whose nature is still unknown.

"It has a spectrum unlike anything else I have ever seen," says Djorgovski. "We have combed the literature and asked all kinds of experts, but no one can tell us what it is. It is the first one of something new—and a complete mystery to us."

Another discovery is objects that can vary in brightness by a large factor. Since the photographs used in DPOSS are taken at different times with different filters, objects that are much brighter at one time would stand out as having peculiar colors. One such discovery is a starlike object which is associated with an extremely faint galaxy.

When the survey photograph was taken, the object was several hundred times brighter than the galaxy itself, perhaps a hundred times brighter than a supernova explosion. Astronomers speculate that it may have been associated with an undetected gamma-ray burst, but it could also be something even more strange and previously unseen.

Astronomers at Caltech and elsewhere are discussing the concept of the future National (or Global) Virtual Observatory, to be built in cyberspace rather than on some mountaintop. This would be a way to organize and combine many of the large new and forthcoming sky surveys and other astronomical data, to make them accessible over the Web, and to provide novel data-mining tools for their scientific exploration.

Astronomers and computer scientists are now starting collaborations to make this vision a reality. This would be a new way of doing astronomy, with a computer and a rich data archive, rather than with a telescope.

"We are really only beginning to explore the universe in some detail. There must be many wonderful new and unexpected things out there, waiting to be discovered, and large sky surveys are the best way to find them," concludes Djorgovski.

In addition to Djorgovski, the Caltech team includes postdoctoral scholars Stephen Odewahn and Robert Brunner, graduate student Roy Gal, and several Caltech undergraduates. Professor of Physics Tom Prince is also one of the leaders of the effort to create the Virtual Observatory. The work on the DPOSS survey is supported by a grant from the Norris Foundation and by other private donors.

Robert Tindol

Caltech observes brightest gamma-ray burst so far

PASADENA-An extraordinarily bright cosmic gamma-ray flash turns out to be the most energetic one measured so far, according to a team of astronomers from the California Institute of Technology.

"The burst appeared to be more luminous than the whole rest of the universe, and that would be very hard to explain by most current theories,"said Caltech professor of astronomy and planetary science Shrinivas Kulkarni, one of the principal investigators on the team.

"It was ten times more luminous than the brightest burst seen so far, and that was quite unexpected."

"If the gamma rays were emitted equally in all directions, their energy would correspond to ten thousand times the energy emitted by our sun over its entire lifetime so far, which is about 5 billion years," said Caltech professor of astronomy S. George Djorgovski, another of the principal investigators on the team. "Yet the burst lasted only a few tens of seconds."

Gamma-ray bursts are mysterious flashes of high-energy radiation that appear from random directions in space and typically last a few seconds. They were first discovered by U.S. military Vela satellites in the 1960s. Since then, over a hundred theories of their origins have been proposed, but the causes of gamma-ray bursts remain unknown. Some theorists believe that the bursts originate during the formation of black holes.

NASA's Compton Gamma-Ray Observatory satellite has detected several thousand bursts so far. The chief difficulty in studying these puzzling flashes is in locating them precisely enough and quickly enough to follow up with ground-based telescopes.

A breakthrough in this field was made in early 1997 by the Italian/Dutch satellite BeppoSAX, which can locate the bursts with a sufficient accuracy. A team of Caltech astronomers was then able to establish that the bursts originate in the very distant universe. Since then, about a dozen bursts have been studied in detail by astronomers using ground-based telescopes.

The bursts may last only a few seconds in gamma rays, but leave more long-lived but rapidly fading afterglows in X-rays, visible light, and radio waves, which can be studied further.

This burst, called GRB 990123, was discovered by the BeppoSAX satellite on January 23. It was the brightest burst seen so far by this satellite, and one of the brightest ever seen by NASA's Compton Gamma-Ray Observatory.

Within three hours of the burst, members of the Caltech team, including senior postdoctoral scholar in astronomy Stephen Odewahn and graduate students Joshua Bloom and Roy Gal, used Palomar Observatory's 60-inch telescope to discover a rapidly fading visible-light afterglow associated with the burst.

"This adventure began at 5 a.m. with a wake-up call from our Italian friends alerting us about their burst detection," said Bloom, "But it was certainly worth it. We got to watch a remarkable fireworks show!"

A comparison of images obtained at Palomar Observatory. The image on the top is from the Palomar Observatory's digital sky survey (DPOSS). The image on the bottom is the discovery image obtained by S. C. Odewahn and J. S. Bloom.

Following the Caltech team's announcement, several hours later a team of astronomers known as the ROTSE collaboration, led by Professor Carl Akerloff of the University of Michigan, reported that the visible light counterpart of the burst was also seen in the images taken with a small, robotic telescope operated by their team, starting only 22 seconds after the burst. This was the first time that such rapid measurement of a burst afterglow was made, and its extreme brightness was unexpected.

Meanwhile, a new radio source, coincident with the visible-light afterglow discovered at Palomar, was found at the National Radio Astronomy Observatory's Very Large Array radio telescope, near Socorro, New Mexico, by Dale Frail and Kulkarni.

Such a radio flash was predicted by Dr. Re'em Sari, a theorist at Caltech, and Dr. Tsvi Piran (now at Columbia University), and it provides an important input for theories of gamma-ray bursts.

At the prompting of the Caltech team, a group of astronomers led by Professor Garth Illingworth of the University of California at Santa Cruz, used the W. M. Keck Observatory's 10-meter Keck-II telescope at Mauna Kea, Hawaii, to obtain a spectrum of the burst afterglow.

A distance to the burst was determined from its spectrum, and the burst was found to be about 9 billion light-years from Earth.

The Keck measurement of the distance was crucial. "We were stunned," said Djorgovski. "This was much further than we expected, and together with the observed brightness of the burst it implied an incredible luminosity.

"The peak brightness of the visible light afterglow alone would be millions of times greater than the luminosity of an entire galaxy, and thousands of times brighter than the most luminous quasars known."

This remarkable light flash contained only a small fraction of the total burst energy in the gamma rays. Caltech astronomers note that even more energy was likely emitted in forms that are difficult to observe, such as gravitational waves or neutrinos, elusive particles that can penetrate the entire planet Earth without stopping.

As the burst's afterglow faded, the Caltech team discovered a faint galaxy adjacent to it in the sky, in infrared images obtained with the W. M. Keck Observatory's 10-meter Keck-I telescope at Mauna Kea.

This is almost certainly the galaxy in which the burst originated. The galaxy is about as faint as an ordinary 100-watt lightbulb would be if seen from a distance of half a million miles, about twice the distance to the moon.

Subsequently, following a proposal by the Caltech team and others, the Hubble Space Telescope obtained visible-light images of this galaxy and the burst's afterglow. The analysis of these images by the Caltech team indicates that the galaxy is not unusual in its properties, compared to other normal galaxies at comparable distances from Earth.

A detailed follow-up study of the burst's afterglow by the Caltech team revealed a change in its brightness that could be interpreted as a sign of a jet of energy, moving close to the speed of light, and pointing nearly toward Earth.

"This was the first time that such behavior was seen in a gamma-ray burst," emphasized Kulkarni, "and it may help explain in part its enormous apparent brightness."

Scientists are still debating whether such a powerful beaming of energy occurs in gamma-ray bursts.

The team's findings appear in the April 1 issue of the scientific journal Nature, and in a forthcoming issue of the Astrophysical Journal Letters.

In addition to Kulkarni, Djorgovski, Odewahn, Sari, Bloom, and Gal, the Caltech team also includes Professors Fiona Harrison and Gerry Neugebauer, Drs. Chris Koresko and Lee Armus, and several others.


Robert Tindol

Caltech astronomer elected president of the American Astronomical Society

PASADENA—Anneila Sargent, professor of astronomy at the California Institute of Technology and director of Caltech's Owens Valley Radio Observatory, has been elected president of the American Astronomical Society (AAS).

Her term of office as president-elect will begin in June, and she will serve as president from June 2000 to June 2002, said AAS spokesperson Steve Maran.

Sargent, a native of Scotland, is an authority on star formation in the Milky Way and other galaxies. Most recently she has been investigating the way in which stars like the sun are created and evolve.

With her collaborators and postdoctoral scholars, she uses the Owens Valley millimeter-wave array, and the Keck Telescopes on Mauna Kea, Hawaii, to search for and study other potential planetary systems. Her interests range from the earliest stages of star formation, when dense cores in interstellar clouds collapse to form stars, to the epochs when individual planets may be born. This field has garnered considerable interest within the scientific community, as well as from the news media and the general public, because of the possibility of locating other worlds outside the solar system.

Sargent cochaired a 1996 workshop at the request of the White House Office of Science and Technology Policy to assess the major questions of space science and how U.S. programs can promote discovery to address those questions, and to plan for future steps in space exploration and research. Titled "The Search for Origins," the workshop report summarized the findings of three dozen of the leading biologists, planetary scientists, astronomers, and cosmologists in the country, and led to a workshop headed by Vice President Al Gore.

Currently, she is also a member of the Board of Associated Universities Inc., the Space Telescope Institute Council, and the National Research Council's decadal astronomy and astrophysics survey committee.

She was also a member of the 1995 Gordon Conference on the Origins of Solar Systems, the 1995 blue-ribbon panel on NASA's proposed exploration of neighboring planetary systems, and the 1993 National Research Council's committee on astronomy and astrophysics, and she was vice-chair of the 1993 NRC task group on the SIRTF and SOFIA infrared space missions.

Born in Kirkcaldy, Fife, Scotland, Sargent earned her bachelor of science degree with honors in physics from the University of Edinburgh. After completing her doctorate in astronomy at Caltech in 1977, she joined the Institute as a research fellow in astronomy, and as a member of the professional staff. She was appointed a senior research fellow in 1988, and a senior research associate in 1990.

She was named associate director of the Owens Valley Radio Observatory in 1992, became executive director in 1996, and director in 1998. During the same year, she was also appointed a professor of astronomy.

Her major honors include the 1998 NASA Public Service Medal, which she was awarded in part for her work on the Space Science Advisory Committee and as a member of the NASA Council. Her Caltech honors include the 1998 Woman of the Year award. She is married to Wallace Sargent, who is also a Caltech professor of astronomy, and director of Palomar Observatory. The Sargents have two daughters, Lindsay Sargent and Alison Hubbs.

Robert Tindol
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New electron states observed by Caltech physicists

PASADENA—Caltech physicists have succeeded in forcing electrons to flow in an unusual way never previously observed in nature or in the lab.

According to James Eisenstein, professor of physics, he and his collaborators have observed electrons that, when confined to a two-dimensional plane and subjected to an intense magnetic field, can apparently tell the difference between "north-south" and "east-west" directions in their otherwise featureless environment. As such, the electrons are in a state very different from that of conventional isotropic solids, liquids, and gases.

"Electrons do bizarre and wonderful things in a magnetic field," says Eisenstein, explaining that electrons are elementary particles that naturally repel each other unless forced together.

By trapping billions of electrons on a flat surface within a semiconductor crystal wafer—and thus limiting them to two dimensions—Eisenstein's team is able to study what the electrons do at temperatures close to absolute zero and in the presence of large perpendicular magnetic fields.

Research on exotic states of electrons is relatively new, but its theoretical history goes back to the 1930s, when Eugene Wigner speculated that electrons in certain circumstances could actually form a sort of crystallized solid. It turns out that forcing electrons to lie in a two-dimensional plane increases the chances for such exotic configurations.

"They cannot get out of one another's way into the third dimension, and this actually increases the likelihood of unusual 'correlated' phases," Eisenstein says. Adding a magnetic field has a similar effect by forcing the electrons to move in tiny circular orbits rather than running unimpeded across the plane.

One of the best examples of the strange behavior of two-dimensional electron systems is the fractional quantum Hall effect, for which three American scientists won the Nobel Prize in physics last year. Electrons in such a system are essentially a liquid, and since the quantum effects of the subatomic world become a factor at such scales, the entire group takes on some unusual electrical properties.

Eisenstein's new findings are very different than the fractional quantum Hall effect. Most importantly, his group has found that a current sent one way through the flat plane of electrons tends to encounter much greater resistance than an equal current sent at a perpendicular angle. Normally, one would expect all the electrons to more or less disperse evenly across the flat plane, which would mean the same resistance for a current flowing at varying angles.

Dramatically, this "anisotropy" only sets in when the temperature of the electrons is reduced to within one-tenth of one degree above absolute zero, the lowest temperature a system can attain.

Owing to the laws of quantum mechanics, the circular orbits of the electrons exist only at discrete energies, called Landau levels. For the fractional quantum Hall effect, all of the electrons are in the lowest such level. Eisenstein's new results appear when the higher energy levels are also populated with electrons. While it appears that a minimum of three levels must be occupied, Eisenstein has seen the effects in many higher Landau levels.

"This generic aspect makes the new findings all the more important," comments Eisenstein.

One scheme that might explain the new results is that the electrons are accumulated into long ribbons. Physically, the system would somewhat resemble lines of billiard balls lying in parallel rows on a pool table. If this is what is happening, the Coulomb repulsion of the electrons is overwhelmed within the ribbons so that the electrons can cram more closely together, while in the spaces between the ribbons the number of electrons is reduced.

"There's not a good theoretical understanding of what's going on," Eisenstein says. "Some think such a 'charge-density wave' is at the heart; others think a more appropriate analogy might be the liquid crystal displays in a digital watch."

Another interesting question that could have deep underpinnings is how and why the system "chooses" its particular alignments. The alignment could have to do with the crystal substrate in the wafer, but Eisenstein says this is not clear.

Eisenstein and his collaborators are proceeding with their work, and have recently published results in the January 11 issue of the journal Physical Review Letters.

Heavily involved in the work are Mike Lilly, a Caltech postdoctoral scholar; and Ken Cooper, a Caltech graduate student in physics. Loren Pfeiffer and Ken West—both of Bell Laboratories, Lucent Technologies in Murray Hill, New Jersey—contribute the essential high-purity semiconductor wafers used in the experiments.

Robert Tindol

David Goodstein Awarded 1999 Oersted Medal

PASADENA—The California Institute of Technology is pleased to announce that David Goodstein has been awarded the 1999 Oersted Medal by the American Association of Physics Teachers. The medal is to be presented at the Association's annual meeting in Anaheim next year.

Goodstein is vice provost and professor of physics and applied physics at Caltech, where he has been on the faculty for more than 30 years. In 1995 he was named the Frank J. Gilloon Distinguished Teaching and Service Professor.

His book, States of Matter, published in 1975 by Prentice Hall and reissued by Dover Press in 1985, was hailed by Physics Today as the book that launched a new discipline, condensed-matter physics. His research in experimental condensed-matter physics has dealt with phases and phase transitions in adsorbed, two-dimensional matter, ballistic phonons in solids, superfluidity in liquid helium, and critical point phenomena. This work has led to nearly 200 scientific publications. He is currently working on a future flight experiment that will examine the dynamics of the superfluid phase transition in the absence of gravity.

Goodstein has served on numerous scientific and academic panels, currently including the national advisory committee to the mathematical and physical sciences directorate of the National Science Foundation, which he currently chairs. He is a founding member of the board of directors of the California Council on Science and Technology.

Goodstein was the host and project director of The Mechanical Universe, a 52-part college physics telecourse based on his popular lectures at Caltech. The project, which has been adapted for high-school use and translated into many other languages, has been broadcast on hundreds of public-broadcasting stations and has garnered more than a dozen prestigious awards, including the 1987 Japan Prize for television.

In recent times, Goodstein has become interested in some of the larger issues that affect science as a profession. In a series of articles, colloquia, and speeches, he has stressed and analyzed the profound changes that became inevitable in the last few decades as the long period of exponential expansion of science came to an end. He has also turned his attention to issues related to conduct and misconduct in science. Prompted by the need to compose a set of regulations governing possible misconduct at Caltech, he has developed an academic subspecialty in this area, writing and speaking about it in a variety of forums. Together with his colleague, Professor of Philosophy James Woodward, he has developed a course, Research Ethics, which has been taught each year at Caltech since the early 1990s.

Born in Brooklyn, New York, Goodstein attended Brooklyn College and received his PhD in physics from the University of Washington. He lives in Pasadena with his wife, Dr. Judith R. Goodstein, who is a faculty associate in history at Caltech, where she serves as archivist and registrar. The Goodsteins have two grown children and two grandchildren and have recently coauthored a best-selling book, Feynman's Lost Lecture.

The Oersted Medal, established in 1936, is the most prestigious award of the American Association of Physics Teachers and recognizes a teacher for notable contributions to the teaching of physics. A monetary award of $5,000, an inscribed medal, and a certificate are presented to the winner. There have been two previous Caltech winners of the Oersted Medal: Robert A. Milliken in 1940 and Richard P. Feynman in 1972.

Sue Pitts McHugh
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Caltech physicists achieve first bona fide quantum teleportation

PASADENA—Physicists at the California Institute of Technology, joined by an international collaboration, have succeeded in the first true teleportation of a quantum state.

In the October 23 issue of the journal Science, Caltech physics professor H. Jeff Kimble and his colleagues write of their success in transporting a quantum state of light from one side of an optical bench to the other without it traversing any physical medium in between.

In this sense, quantum teleportation is similar to the far-fetched "transporter" technology used in the television series Star Trek. In place of the actual propagation of a light beam, teleportation makes use of a delicate quantum mechanical phenomenon known as "quantum entanglement," the quintessential ingredient in the emerging field of quantum information science.

"In our case the distance was only a meter, but the scheme would work just as well over much larger distances," says Professor Samuel Braunstein, a coauthor from the University of Wales in Bangor, United Kingdom, who, with Kimble, conceived the scheme. "Our work is an important step toward the realization of networks for distributing quantum information—a kind of 'quantum Internet.'"

Teleportation of this kind was first proposed theoretically by IBM scientist Charles H. Bennett and colleagues in 1993. The Caltech experiment represents the first time quantum teleportation has actually been performed with a high degree of "fidelity." The fidelity describes how well a receiver, "Bob," can reproduce quantum states from a sender, "Alice."

Although quantum teleportation was recently announced by two independent labs in Europe, neither experiment achieved a fidelity that unambiguously required the use of quantum entanglement between Alice and Bob.

"True quantum teleportation involves an unknown quantum state entering Alice's apparatus and a similar unknown state emerging from Bob's remote station," says Kimble. "Moreover, the similarity of input and output, as quantified by the fidelity, must exceed that which would be possible if Alice and Bob only communicated by classical means—for instance, by normal telephone wiring.

"Although there has been wonderful progress in the field, until now there has not been an actual demonstration of teleportation that meets these criteria."

In the experiment, the Caltech team generated exotic forms of light known as "squeezed vacua," which are split in such a way that Alice and Bob each receive a beam that is the quantum mechanical "twin" of the other. These EPR beams, named after the historic Einstein-Podolsky-Rosen (EPR) paradox of 1935, are among the strangest of the predictions of quantum mechanics. It was their theoretical possibility that led Einstein to reject the idea that quantum mechanics might be a fundamental physical law.

A trademark of quantum mechanics is that the very act of measurement limits the controllability of light in ways not observed in the macroscopic world: even the most delicate measurements can cause uncontrollable disturbances. Nevertheless, in certain circumstances, these restrictions can be exploited to do things that were unimaginable in classical physics.

Here, photons from the EPR beams delivered to Alice and Bob can share information that has no independent existence in either beam alone. Through this "entanglement," the act of measurement in one place can influence the quantum state of light in another.

Once Alice and Bob have received their spatially separate but entangled components of the EPR beams, Alice performs certain joint measurements on the light beam she wishes to teleport together with her half of the EPR "twins." This destroys the input beam, but she then sends her measurement outcomes to Bob via a "classical" communication channel. Bob uses this classical information to transform his component of the EPR beam into an output beam that closely mimics the input to Alice, resurrecting at a distance the original unknown quantum state.

A unique feature of Kimble's experiment is a third party called "Victor," who "verifies" various aspects of the protocol performed by Alice and Bob. It is Victor who generates and sends an input to Alice for teleportation, and who afterward inspects the output from Bob to judge its fidelity with the original input.

"The situation is akin to having a sort of 'quantum' telephone company managed by Alice and Bob," says Kimble. "Having opened an account with an agreed upon protocol, a customer (here Victor) utilizes the services of Alice and Bob unconditionally for the teleportation of quantum states without revealing these states to the company. Victor can further perform an independent assessment of the 'quality' of the service provided by Alice and Bob."

The experiment by the Kimble group shows that the strange "connections" between entities in the quantum realm can be gainfully employed for tasks that have no counterpart in the classical world known to our senses.

"Taking quantum teleportation from a purely theoretical concept to an actual experiment brings the quantum world a little closer to our everyday lives," says Christopher Fuchs, a Prize Postdoctoral Scholar at Caltech and a coauthor. "Since the earliest days of the theory, physicists have treated the quantum world as a great mystery. Maybe making it part of our everyday business is just what's been needed for making a little sense of it."

This demonstration of teleportation follows other work the Kimble group has done in recent years, including the first results showing that individual photons can strongly interact to form a quantum logic gate. Kimble's work suggests that the quantum nature of light may someday be exploited for building a quantum computer, a machine that would in certain applications have computational power vastly superior to that of present-day "classical" computers.

Robert Tindol

Tom Apostol Wins Trevor Evans Award

PASADENA—Dr. Tom Apostol, professor emeritus of mathematics and project director of Project MATHEMATICS! at the California Institute of Technology, was recently named a recipient of the Trevor Evans award by the Mathematical Association of America.

Apostol was awarded the prize in recognition of his article "What Is the Most Surprising Result in Mathematics? (Part II)" (Math Horizons, February 1997).

According to the award citation, the answer to Apostol's question is "the Prime Number Theorem. At least that is the answer so convincingly argued by Tom Apostol in this information-rich yet easily digestible article. The article traces the history of the theorem and shows how the riddle of the distribution of the primes drove Euler, Riemann, and many others to unearth fertile new areas of mathematics. Apostol reminds us that deep ideas can always be made accessible to young minds—you just have to try hard enough."

Apostol received a BS (1944) and an MS (1946) from the University of Washington, and a PhD (1948) from the University of California, Berkeley. He has been a professor at Caltech since 1950.

Established in 1992, the Trevor Evans awards, consisting of a citation and cash prize, are presented by the Mathematical Association of America to authors of exceptional articles that are accessible to undergraduates and published in Math Horizons.

The Mathematical Association of America (MAA) is the world's largest organization devoted to mathematics education at the collegiate level. The nearly 30,000 members of the MAA participate in a variety of activities that foster mathematics education, professional development, student involvement, and public policy. MAA's national focus is complemented by its 29 regional sections—together functioning as an extensive network for the mathematics community.

Founded in 1891, Caltech has an enrollment of some 2,000 students, and a faculty of about 280 professorial faculty and 130 research faculty. The Institute has more than 19,000 alumni. Caltech employs a staff of more than 1,700 on campus and 5,300 at JPL.

Over the years, 26 Nobel Prizes and four Crafoord Prizes have been awarded to faculty members and alumni. Forty-three Caltech faculty members and alumni have received the National Medal of Science; and eight alumni (two of whom are also trustees), two additional trustees, and one faculty member have won the National Medal of Technology. Since 1958, 13 faculty members have received the annual California Scientist of the Year award. On the Caltech faculty there are 75 fellows of the American Academy of Arts and Sciences; and on the faculty and Board of Trustees, 68 members of the National Academy of Sciences and 46 members of the National Academy of Engineering.

Sue Pitts McHugh
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Thomas Tombrello named Caltech PMA division chair

PASADENA—The California Institute of Technology Board of Trustees has approved the appointment of physics professor Thomas A. Tombrello chair of the Division of Physics, Mathematics and Astronomy.

Tombrello's appointment becomes effective August 1, 1998, according to Caltech president David Baltimore.

"Tom Tombrello has demonstrated remarkable abilities in both research and administration through the years," Baltimore said. "Not only does he pursue a huge variety of interests, but he is also equally at home with basic and applied research.

"He's the ideal person to lead the division into the 21st century."

Tombrello and his research group are primarily involved in applying the techniques of theoretical and experimental physics to problems in materials science, surface physics, and planetary science. His ongoing research includes understanding the damage processes caused by megavolt ions in solids, characterizing the sputtering of materials by low-energy ions, and growing and studying novel light-emitting materials.

A native of Texas, Tombrello was born in Austin, grew up in Dallas, and earned his BA, MA, and PhD degrees at Rice University in Houston.

Tombrello came to Caltech in 1961, and except for a brief stint on the Yale faculty, has been here ever since. A full professor of physics since 1971, he also served as vice president and director of research at Schlumberger-Doll Research from 1987 to 1989. He was named William R. Kenan Jr. Professor at Caltech in 1997.

As chair of the Division of Physics, Mathematics and Astronomy, he will oversee a department that has long been acclaimed for groundbreaking research and outstanding faculty. The department's list of Nobel laureates includes Robert A. Millikan, who measured the charge of the electron; Carl Anderson, who discovered the positron and thus demonstrated the existence of antimatter; Richard Feynman, who revolutionized the theory of quantum electrodynamics with his Feynman diagrams; Murray Gell-Mann, who first predicted the existence of the quark as well as the quantum concept of strangeness; and William A. Fowler, who was one of the founders of the field of nuclear astrophysics.

Tombrello said that his immediate goals will be to strengthen the Division's efforts in theoretical physics, mathematics, and observational astronomy.

Robert Tindol

Physics student wins acclaim for new theory of neutron-star spin

PASADENA--When you're beginning a career in cosmology, it's only fitting to start with a bang.

That's what Ben Owen will do now that he has his doctorate in physics from the California Institute of Technology. Not only did Owen win the annual Clauser Prize for the best Caltech dissertation at the June 12 commencement, but his work has also been the subject of an international symposium. In September, he'll fly to Germany for a new job at the Albert Einstein Institute (where the symposium was held) as a postdoctoral researcher.

The reason Owen's dissertation has stirred so much interest is that it solves a nagging, decades-old question in astrophysics and opens up vistas of new questions.

In particular, chapter 5 of his "Gravitational Waves from Compact Objects" shows why young neutron stars have such slow spins. The research of chapter 5, which was done with Lee Lindblom and Sharon Morsink, predicts that rapidly spinning, newborn neutron stars will pulsate wildly, throwing off their spin energy as gravitational waves. The work appears in the June 1 issue of the journal Physical Review Letters.

The new theory of Owen and his colleagues will be tested experimentally in a few years, after the Laser Interferometer Gravitational-Wave Observatory (LIGO) comes on-line.

Neutron stars are extremely compact bodies about the mass of the sun, packed into a sphere about 15 miles in diameter. They are typically formed in the supernova explosions of massive stars.

Because the fusion of lighter elements in the star has ceased, the material remaining after the explosion scrunches together so closely that the electrons and protons of most of its atoms actually fuse together to form neutrons—and thus the name.

Neutron stars are not so compact as black holes, which are regions so dense that not even light can escape. But neutron stars are still compact enough to generate some bizarre effects. If an astronaut landed on a neutron star, for example, both he and his spaceship would be smeared by gravity into an even layer of just a few atoms over the entire surface of the star.

Also, neutron stars are noteworthy for their tendency to spin like crazy. Astronomers on Earth infer this spin from a telltale "blinking" in radio signals or sometimes even in a strobelike blinking in visible light. Based on the rate of blinking, observers know that these particular neutron stars—known as pulsars—can spin as rapidly as 600 times per second.

But this is where the controversy comes in and where Owen's dissertation is stirring up so much interest. Based on the laws of Newtonian physics, there's no compelling reason why a slowly rotating normal star shouldn't speed up to the fastest rotation rate possible once it goes supernova and then collapses into a neutron star.

The same effect can be seen in an ice skater who pulls in her arms to rotate faster while spinning.

But all of the young neutron stars observed by astronomers spin at 120 revolutions per second or less—a factor of five slower than the fastest known pulsar, which is very old and is thought to have been spun up long after the supernova by other mechanisms.

Owen's theory is that a type of fluid circulation occurs on the neutron stars that creates a sort of drag in space-time. Called "r-modes" because they owe their existence to rotation, these motions look much like the ocean eddies that move currents in circular motions on Earth.

What Owen's dissertation has shown is that the r-modes of a rapidly rotating neutron star strongly emit gravitational waves. The drag effect, caused by the gravitational waves leaving the star, in turn causes the r-modes to grow when they would normally die away due to the internal friction found in young neutron stars. In the process, this forces the spinning neutron star to slow down.

Thus, newly created neutron stars can indeed start their lives spinning quite rapidly, but are quickly slowed down by the growing r-modes. Old neutron stars have much stronger friction and can be spun up again by other processes.

"The standard methods known right now say that these currents could grow very large," says Owen.

The size of the r-modes is the key, he explains. His work shows that, if an r-mode were to be so large that it sloshed material virtually from pole to pole, the neutron star should slow down to one-tenth its original rate of rotation within a year. This, in fact, conforms to the rates of rotation seen in existing pulsars.

But the effect is a self-defeating one, Owen says. The r-modes are kept going by gravitational waves, which are stronger when emitted by rapidly rotating stars. But the gravitational waves leaving the star cause it to spin down, which makes the waves weaker, which in turn means there is less power to keep the r-modes going. So the neutron star eventually reaches an equilibrium.

"If the r-modes get very large, they'll start radiating a lot of energy as gravitational waves," Owen says. "But they can't do that forever, because the rotational energy they're radiating is what keeps them alive in the first place."

So in the course of a year, Owen shows, just about any pulsar should be spun down to a rotation rate much less than the Newtonian maximum.

Owen's work is purely theoretical at this point, but could be tested when LIGO is operational. LIGO, a collaborative project between Caltech and MIT with twin detectors in southern Louisiana and central Washington, is designed expressly for the detection and detailed study of gravitational waves.

If a supernova goes off in our cosmic neighborhood-say, within 60 million light-years-LIGO should be able to detect the gravitational waves thrown toward Earth. And if the waves change at the predicted rate over the course of a year, Owen's theoretical work will be borne out by observation.

"Several supernovae should go off every year at a distance close enough for LIGO to detect the waves," he says. "So when a supernova occurs, we should first see the waves start very abruptly at up to 1,000 cycles per second, and then chirp down to about 100 to 200 cycles per second over the course of a year."

The work of Owen, Lindblom and Morsink raises a vista of new questions, with which cosmologists and gravity-wave experimenters world-wide are now struggling. Just how large does the sloshing in a young neutron star get, and what limits its growth? Can LIGO experimenters redesign their computer programs to find Owen's predicted waves in LIGO's plethora of data? What other kinds of stars will slosh wildly, like Owen's newborn neutron stars, and what will that sloshing do to them, and can LIGO be tuned to find their gravitational waves?

Owen's thesis supervisor at Caltech was Kip Thorne, a renowned theoretical physicist who is author of the popular book Black Holes and Time Warps: Einstein's Outrageous Legacy.

Robert Tindol
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