Experimental Optical Physics

Researchers in optical physics explore the interaction of light with matter by using and developing light sources that span the electromagnetic spectrum from the microwave to the X-ray region. This research is motivated by a wide variety of interests including the desire to understand fundamental features of nature, such as conceptual foundations of quantum mechanics at one extreme, and technology-oriented applications, such as biomedical imaging or optical communications, at the other.

Quantum Optics

Ultrastable Optical Trapping of Neutral Fermions

[Mike Gehm and Ming Shien Chang]

Graduate students Mike Gehm and Ming Shien Chang adjust the optics in their laser beam experiment.

The Quantum Optics group at Duke has a large program on the cooing and trapping of neutral fermions. A central feature of this program is the first stable all-optical trap which the group has developed. All-optical traps are very well suited for tightly confining neutral atoms and molecules over very long periods of time. The simplest all-optical trap consists of just a single laser beam, tightly focused into an ultrahigh vacuum system. Atoms or molecules are attracted to the high intensity region, which provides a confining potential. By detuning the laser far below resonance, the confining forces are made nearly quantum state independent, and optical scattering (with its associated heating) is suppressed. Although such optical traps have relatively weak confining forces, they are readily loaded by precooling the atoms or molecules using the now standard laser methods.

Unfortunately, optical traps have been plagued for many years by unexplained heating rates that have limited the trap lifetime to just a few seconds. Recently, the Quantum Optics group showed theoretically that optical traps are very sensitive to intensity and pointing noise in the trapping laser beam. Using this knowledge, the Duke group developed the first ultrastable optical trap. The trap is based on an ultrastable CO2 laser. For CO2 laser traps, the extremely large detuning from resonance and the very low optical frequency lead to optical scattering rates that are measured in photons per atom per hour. Hence, optical heating is negligible. The observed 1/e trap lifetime is 370 seconds, consistent with time an atom can spend in the trap in a vacuum of 10-11 Torr before being kicked out by a the background gas collision. The trap lifetime is, by nearly two orders of magnitude, the longest ever achieved with an all-optical trap, comparable to the best reported magnetic traps.

The new trap has wide applications in the study of many-body quantum dynamics. For example, starting from a low temperature atomic gas, it will be possible to coherently create and trap bound molecules, enabling ``superchemistry.'' Currently, the new trap is being used to study two-state mixtures of an ultracold fermionic gas of 6Li. This system has been predicted to under a pairing transition at sufficiently low temperatures, providing an analog of high temperature superconductivity in an atomic vapor. Since the temperature, density and interaction strength of the vapor are all adjustable, important new tests of superconductivity theory will be possible.

Faculty Research Interests

Professor John E. Thomas
(Ph.D. MIT, 1979) is developing new techniques based on resonance imaging in optical force fields for precision position measurement of moving atoms in beams and traps. These methods will find applications in atomic lithography, atom interferometers, atom optics, and in fundamental experiments on atomic statistics. Ongoing experiments include imaging of cold trapped atoms. Measurement of the spatial distributions and spatial correlations on an atomic de Broglie wavelength scale are expected to reveal many new features of weakly interacting Bosons and Fermions.

Quantum Electronics

The Duke Quantum Electronics laboratory is involved in a diverse set of research projects in the areas of quantum optics, nonlinear optics, control and synchronization of chaos in optical and electronic systems, and characterizing and controlling the dynamics of biological systems. In the area of nonlinear optics, the researchers are developing a new type of all-optical switch based on the formation of transverse optical patterns. Interesting nonlinear and quantum optical effects are also being studied in a highly-anisotropic two-dimensional magneto-optical trap (MOT). This MOT traps a sample of cold atoms that is several cm long and provides sufficient optical depth to explore novel interactions between light and matter.

The Quantum Electronics Laboratory is also exploring methods to enhance nonlinear optical processes in optical fiber systems. Using Stimulated Brillouin Scattering (SBS), we have demonstrated slow and stopped light in optical fiber using commercial telecom devices and off-the-shelf components.

Faculty Research Interests

Professor Daniel J. Gauthier
(Ph.D. Institute of Optics, U. Rochester, 1989) is interested in highly nonlinear matter-light interactions where standard perturbation techniques fail to adequately explain the observed behavior. He is studying various quantum optical systems that smoothly span the range in scale from microscopic (where quantum fluctuations are paramount) to macroscopic (where the behavior is nearly deterministic). He is currently developing an entirely new class of quantum oscillators, which are unique in that they are based on two-photon rather than one photon stimulated emission processes. Over the next several years, ongoing projects will explore two-photon lasers, controlling chaos in optical systems, and cavity quantum electrodynamics with cooled and trapped atoms.