Xiyue Miao

Benjamin Dietzek

In Professor Metcalf's group various experimental studies of optical control of atomic motion are undertaken. These include extraordinarily large forces in non-monochromatic light, ultra-sensitive methods for measuring atomic velocity distributions, and the study of fascinating dark states.

Strong Forces: Until very recently, most laser cooling experiments were done using multiple light beams, each having the same, single frequency (often made with mirrors). The cooling forces were then limited to Frad = hkg/2. But in polychromatic light an extra degree of freedom appears as d, the separation between frequencies or the modulation range or whatever characterizes the spectrum. Then the force is hkd/2, and since d can be >> g, these forces can be huge. The exchange of momentum between the atom and the light field can be coherently controlled.

Velocimetry: Recently we have developed Stimulated Optical Compton Scattering as a tool for velocimetry. It has resolution of about the recoil velocity, and only perturbs the atomic sample on the recoil scale. It may be further extended to 3-D, as well as developed into a recoil-induced Faraday effect. Thus it may be used in situ, without destruction of the sample.

Dark States: Dark states do not absorb light, even if it is very strong and tuned to atomic resonance. These fascinating phenomena arise from superposition of external momentum states, and thus constitute atoms travelling in two directions at once. The concepts strike right at the "heart of quantum mechanics" as espoused by Schroedinger, and can lead to unlimited low temperatures. We have observed such states in systems as simple as a two-level atom.

	Seung-Hyun Lee.