Creating new states of matter with cavity QED: From photoassociation to spintronics

Cavity quantum electrodynamics (QED) is one of the main tools of physicists to explore the non-classical quantum world. The high quality factors of modern optical cavities combined with the ability to achieve strong coupling between a cavity mode and a single quantum emitter have made cavity QED the perfect laboratory for exploring unitary quantum mechanics with an eye towards directly testing fundamental principles of quantum mechanics and developing quantum information processing devices. Traditional studies of cavity QED have focused on achieving the strong coupling regime where the quantum mechanical interaction with the vacuum field is stronger than all decay processes. Experiments have only recently demonstrated continuous strong coupling to an individual two-level emitter in the optical regime. Here we propose a research program that studies new applications of cavity QED based on novel extensions of the Jaynes-Cummings model. Just as cavity QED has evolved along two tracks based on the type of emitter and cavity, atoms in a Fabry-Perot cavity or quantum dots grown inside of a semiconductor microcavity, the proposed research will look at new applications in both areas. Specifically, the proposed research will develop new theoretical models to describe Raman photoassociation of ultracold atomic gases via a cavity field. The coherent quantum dynamics of quantum degenerate ultracold gases along with the feedback of an optical resonator lead to a novel nonlinear quantum system that mixes atomic, molecular, and optical waves. The feedback effects of a driven cavity mode provides an extra level of control over the photoassociation dynamics that will lead to precise control over the number of molecules created or dissociated in a way that is impossible using conventional free space photoassociation. A semiclassical analysis of this system by the PI already indicates the presence of bifurcations and bistable regimes. The PI plans to develop and investigate a fully quantum model of cavity assisted photoassociation (CAP). Of particular interest will be the effect of quantum noise on the semiclassical bifurcations and bistable states. The second direction will be to study a single quantum dot embedded in an optical microcavity with electrical leads connected to the dot that allow controlled charging of the dot. The possibility of electrical current fowing through a cavity coupled dot opens up new directions, which have hitherto not been considered. The PI has recently shown that such a system can be an efficient source of pure spin current. The ability to use the cavity field to control the spin current and its statistics will be explored.