Twenty-First Century Chair in Nanotechnology

Fellow, American Physical Society, 2005

Fellow, Optical Society of America, 2005

NSF Young Investigator Award, 1994.

Alumni Distinguished Service Award for Research, 1998.

Ph.D., U. Texas, Austin, 1988

Postdoctoral Associate, M.I.T. 1988-1990.

Assistant Professor to Professor, 1990-98.

Professor Xiao did his Ph.D. research under Professor Jeff Kimble (now at Cal Tech) and joined the University of Arkansas in 1990. He has published extensively in experimental and theoretical quantum optics, laser physics, nonlinear optics, and atomic physics. His research projects are currently funded by the National Science Foundation and the Office of Naval Research.

QUANTUM/NONLINEAR OPTICS WITH MULTI-LEVEL SYSTEMS AND OPTICAL PROPERTIES OF SEMICONDUCTOR NANOSTRUCTURES

Our research group has been working on a broad spectrum of research projects, ranging from fundamental quantum optics to applied optics. In the following, a few current research directions are briefly described. Detail information about our research group and recent publications can be found in our Research Home Page.

1. Atomic coherence effects in multi-level atomic systems. When coherent laser fields interact with multi-level atomic systems, coherence or quantum interference between different atomic energy levels can be induced. We experimentally demonstrated and theoretically explained the effects of electromagnetically induced transparency (EIT) with weak cw diode lasers in three-level cascade-type and lambda-type systems in rubidium atoms under two-photon Doppler-free conditions. We measured the dispersion properties of the EIT system, demonstrated enhancement of four-wave mixing processes in multi-level atomic systems, and measured the enhanced Kerr nonlinear index due to the induced atomic coherence. Using such properties of reduced absorption, sharp dispersion, and greatly enhanced nonlinearity in the multi-level EIT systems, we can demonstrate interesting effects, such as controllable all-optical switching/routing and efficient multi-wave mixing.
   
   By placing such multi-level atoms inside an optical cavity, we have observed and studied bistable and multistable hysteresis loops (in the input-output cavity field intensities) with controllable shape, threshold, rotation direction, and area. These phenomena are much richer and more interesting in the three-level EIT system than their counterparts in the system with two-level atoms inside an optical cavity. Recently, we demonstrated dynamical instability and route to chaos via period doubling in this composite system of a three-level EIT medium inside an optical ring cavity.
2. Optical properties of semiconductor nanostructures. We have been working on optical properties of MBE-grown semiconductor nanostructures and chemically-synthesized colloidal nanocrystals. In the past few years, we measured polarization spectroscopy of single colloidal CdSe quantum rods and demonstrated transition from a zero-dimensional quantum-dot structure to a one-dimensional quantum-wire structure. We showed a potential application of colloidal nanocrystals as a gas sensor for different chemicals and demonstrated the effects of environments, such as a reflective semiconductor surface and a photonic crystal, on the lifetime of the nanocrystals, which demonstrated the ability to control the optical properties of the nanocrystals. Such controllability can be very useful for their potential applications in biological labeling and opto-electronic devices. Recently, we investigated various optical properties of colloidal (spherical) quantum-well nanostructures and observed random lasing action in such medium.
   
   We investigated carrier transfer and quantum tunneling between quantum dots in vertically-aligned double-stacked InAs/GaAs quantum-dot layers and three-dimensionally-ordered quantum-dot arrays. We also observed transition from a zero-dimensional quantum-dot system to a one-dimensional quantum-wire system in a MBE-grown dot-chain nanostructure with elevated temperature and transition from a one-dimensional quantum-wire array to a two-dimensional quantum-well system due to thermally excited carrier transfer. The goal is to design better opto-electronic devices with improved speed, compact size, higher efficiency, and easier integration.