B-E Condensates, Quantum Computing Highlight 1996 DAMOP Meeting
The latest results in Bose-Einstein condensation experiments, quantum resonance imaging and computing, and collision studies of laser-cooled atoms were among the highlights of the annual meeting of the APS Division of Atomic, Molecular and Optical Physics (DAMOP), held 15-18 May at the University of Michigan in Ann Arbor. In addition to the 12 invited symposia featured in the regular technical program, there was a conference banquet held on Friday, May 17, which included the presentation of prizes and awards, as well as an after-dinner lecture by Patrick Seitzer of University of Michigan's Department of Astronomy entitled, "Hubble Space Telescope: Tragedy to Triumph."
Advances in Bose-Einstein Condensates. Bose-Einstein condensates (BECs) comprise a unique state of matter in which gas atoms, cooled to near-absolute-zero temperatures, overlap with each other and collapse into a common quantum state, where they behave essentially as a single "superparticle." Studies of Bose-Einstein condensates promise important insights into the strange world of quantum mechanics, and the future possibility of technologically useful inventions.
Building on over 20 years of experimental work in atomic and optical physics, a research team at the National Institute of Standards and Technology (NIST) and the University of Colorado announced last summer that they had achieved Bose-Einstein condensation in a gas of about 2000 rubidium atoms.
In a Saturday morning session, Wolfgang Ketterle and his MIT colleagues announced that they had produced a Bose-Einstein condensate of 5 million atoms, 10 times bigger than any previous BEC. At 150 microns long and 8 microns wide, the condensate was large enough to be directly observed for the first time, and lasted for 20 seconds. The MIT researchers imaged the BEC with scattered laser light with a sensitive camera. Interestingly, the BEC acts as a lens in the experiments, allowing light to pass through but bending it by a small degree.
The MIT group also found that the light scattered off the condensate is anisotropic. To produce the condensate, the researchers used a combination of lasers and magnetic fields in a special configuration in which cloverleaf-shaped coils generate magnetic fields that tightly confine the atoms while allowing the setup's 11 laser beams to pass easily into the trapping region.
The NIST-University of Colorado team, led by Eric Cornell and Carl Wieman, has found that theory agrees with experiment in its predictions of the Bose-Einstein condensate's critical temperature, the temperature below which atoms in a gas enter the Bose-Einstein condensate phase. Dan Kleppner of MIT described a new technique that greatly improves the ability to monitor atomic transitions in trapped hydrogen. Achieving BEC in hydrogen has been a goal for many years. What has hampered efforts has been the difficulty of monitoring and controlling trapped hydrogen, since the lasers need to manipulate hydrogen energy transitions must deliver ultraviolet light and need development.
Randall Hulet of Rice University described a new trap, employing permanent magnets, that creates a combination of temperature and density in lithium atoms believed to be several hundred times better than that needed to create Bose-Einstein condensation. Surprisingly, Hulet's team is finding that only a small fraction of the atoms in the trap appear to display the signature for BEC. Lithium is different from the other atoms used to produce BEC in that lithium atoms in a gas are slightly attractive toward one another rather than repulsive.
Quantum Computing. In a Friday morning session, C. Monroe of the National Institute of Standards and Technology in Boulder, Colorado, reported on progress toward the development of useful quantum computers and described the experimental challenges that lie ahead. An attractive architecture for such a device is a collection of trapped ions, where two internal states of each ion carry one quantum bit (qubit) of information. A challenge is to scale the system to a string of many trapped ions so that the device can host many more than two qubits.
Collisions of Laser-Cooled Atoms. Advances in laser cooling of neutral atoms have made possible a new form of high resolution spectroscopy known as photoassociation colliding neutral atoms confined in a laser trap are photoassociated to bound excited states of the dimer molecule by absorbing a photon from a tunable laser. The technique can probe long range molecular states that are difficult or impossible to detect by traditional means, and, because of the extremely low energy of the colliding atoms, it is capable of high resolution. Recent results include the first direct, and most precise, measurements of molecular dissociation limit, and the first observation of retardation effects in atom-atom interactions, high precision measurements of atomic lifetimes, and the study of exotic states of alkali dimers.
Quantum Resonance Imaging. Spurred by the advent of laser cooling and trapping, physicists at Duke University are developing new high resolution atom imaging methods, based on resonance imaging in ultrahigh gradient potentials due to optical force fields. According to John Thomas, his group has demonstrated spatial resolution of 200 nm, and the force exerted by the potential is sufficiently large that the atomic momentum can be altered during the measurement. Using new pulsed atom imaging methods in this regime, he believes that "quantum snapshots" of cold atoms in microtraps should soon be possible.
Atomic Beam Magnetic Resonance. Researchers at Ohio State University are developing new ways to study vortex lattices in both low- and high-temperature superconducting samples using atomic beam magnetic resonance technology. Dissipative vortex motion is the major obstacle to many envisioned high-temperature superconducting commercial applications, as well as a source of novel physical phenomena.
According to Gregory Lafyatis, the basic idea is to pass atoms very close to the surface of a superconductor that is penetrated by a magnetic field. In its rest frame, an atom will see a fluctuating magnetic field that is determined by the pattern of magnetic vortices at the superconductor's surface and the velocity of the atom. "If the fluctuating field has a frequency component coincident with a magnetic transition of the atom, the transition may be driven," he said. "Turning things around, by measuring the transition probability for an atom passing over the superconductor as a function of velocity, we are able to study the vortex lattice itself."
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