Graham P. Collins

Quantitative BEC Results Reported at DAMOP Meeting

Now that the rantare of simply creating a Bose–Einstein condensate in a dilute atomic gas has died down (see the “Reference Frame” column by Daniel Kleppner on page 11), the leading research groups are proceeding in earnest to map out the properties of their condensates. Four experimental groups reported their latest results in invited talks at a session on Bose–Einstein condensation (BEC) at the meeting of the American Physical Societys Division of Atomic and Molecular Physics (DAMOP) held in Ann Arbor in May.

STM Rounds up Electron Waves at the QM Corral

Everyone who has completed an elementary quantum mechanics course has seen plots of solutions of the Schrodinger equation for the archetypal “particle in a box.” Now IBM researchers have used scanning tunneling microscopy to image the rippled density of states of electrons inside a “corral” built with a few dozen carefully positioned iron atoms on a copper surface. (See the cover of this issue.) The spectacular results closely match theoretical models of the system.

Experimenters Produce New Bose–Einstein Condensate(s) and Possible Puzzles for Theorists

If the creation of a gaseous Bose–Einstein condensate in Boulder, Colorado, last summer marked the opening of a door to a new world of physics—the realm of wealdy interacting, quantum degenerate atomic gases—then today we have unlocked multiple entrances to that domain. Furthermore, each entrance has a different architecture and looks out across a unique landscape.

Quantum Cryptography Defies Eavesdropping

Students of physics can be Students of physics can be excused for finding their quantum mechanics courses a little cryptic from time to time. Now researchers are using the properties of quantum mechanics to encrypt information for secure transmission.

Sodium Atoms Kicked by Standing Waves Provide a New Probe of Quantum Chaos

The question of how to quantize a system whose classical dynamics is chaotic has long been a puzzle. The hallmark of classical chaos is sensitive dependence on initial conditions: A small perturbation of the system changes its evolution in a way that grows exponentially with time. But in quantum mechanics a small perturbation of the initial state will in general be mapped into a small perturbation of the final state. In reeveral cent years the study of quantum systems whose underlying classical dynamics is chaotic has been an active area of research.

Making Stars to See Stars: DOD Adaptive Optics Work is Declassified

Since the 1970s, researchers working first for the Defense Advanced Research Projects Agency and later under the aegis of the Strategic Defense Initiative have been developing and testing adaptive optics systems—systems for nullifying the effects of atmospheric turbulence on light that passes through it. In May 1991, to the delight of the astronomical community, much of the work became declassified. Adaptive optics works by measuring the distorting effects of the atmosphere on the light from a guide star and adjusting a deformable mirror to conjugate these effects. In particular, the declassified research involves the use of laser beams to create one or more artificial beaconsin the sky to act as guide stars.

Fractionally Charged Quasiparticles Signal Their Presence with Noise

To particle physicists, the electron is the quintessential example of an elementary particle: The highest energy experiments to date have revealed no evidence of any internal structure, no evidence that an electron is made up of some other, more fundamental components. But for condensed matter physicists studying the behavior of matter at low temperatures in semiconductor crystals, electrons can play by a different (although ultimately equivalent) set of rules. The fractional quantum Hall effect, for example, can be explained by invoking quasiparticles, which behave like distinct particles that each carry a fraction of an electrons charge. (On a more fundamental level, quasiparticles are collective excitations of interacting electrons.) Two recent experiments in Israel and France have added to the evidence that these quasiparticles exist.

Supersymmetric QCD Sheds Light on Quark Confinement and the Topology of 4‐Manifolds

Perturbation theory has long been one of the most successful tools in quantum field theory. The technique produces a series of terms, and ideally most of the “physics” is captured by the more readily computed early teims in the expansion, with later terms supplying progressively more negligible corrections. In contrast to such approximations, exact computations in four‐dimensional quantum field theory have been few and far between. As Stephen Shenker (Rutgers University) puts it, “The conventional wisdom was that exact results in four‐dimensional quantum field theory were essentially unobtainable.” This lack of analytic results has been particularly problematic for the theory of quark confinement, which involves the strong force in a thoroughly nonperturbative regime.

Gaseous Bose–Einstein Condensate Finally Observed

About seven decades ago Satyendra Nath Bose and Albert Einstein predicted that a gas of noninteracting integer‐spin particles would condense into a macroscopic quantum state when cooled below a critical temperature. Of course Bose–Einstein condensation (BEC) has long since been seen in superfluid 4He and superconductors, but the condensing systems in these examples are far from being noninteracting gases; relatively strong interactions between the condensing particles greatly complicate the theoretical analysis and the experimental behavior. For more than 15 years groups have been cooling and compressing clouds of atoms on a quest to produce and observe a Bose–Einstein condensate in a nearideal gas. They pushed their devices to the limit, seeking to traverse 15 orders of magnitude of phase‐space density, and as each technique proved insufficient they developed ingenious variations to create ever colder and denser states.

Tabletop Capillary‐Discharge Soft‐X‐Ray Laser Demonstrated

Optical‐wavelength lasers are ubiquitous, from the checkout scanner at the supermarket to the CD player in your Discman. They come in all sizes, all the way down to microelectronic scales. Lasers operating at wavelengths shorter than 100 nanometers, however, have been rare and expensive behemoths ever since their first demonstration a decade ago; they rely on bulky, high‐powered optical lasers to produce the plasma conditions needed for x‐ray lasing.