****Technical abstract**** This project focuses on the new and growing field of exciton-polariton condensates in semiconductor microcavities. Several experimental groups around the world have now shown behavior of exciton-polaritons which is exactly analogous to Bose-Einstein condensation (BEC), including quantized vortices, a bimodal momentum distribution, superfluid flow, Josephson junction oscillations, and linear Bogoliubov excitation spectra. Our group in Pittsburgh has also shown BEC behavior, using a harmonic potential trap created using our unique method using applied stress. Our proposed work will use several new experimental methods, including stabilized lasers to reduce fluctuations, simultaneous real-space and momentum-space imaging of the polaritons, and streak camera temporal imaging, and will use new ultra-high-Q cavities with world record polariton lifetimes (including our present structures which have Q-factor of over a million and diffusion lengths of hundreds of microns). This work is in collaboration with the fabrication group of L. Pfeiffer at Princeton; we will develop new types of structures including etched features acting as barriers for the polaritons. The project will support two Ph.D. students to learn cutting-edge methods of modern optics, including ultrafast and nonlinear optics, design, and fabrication methods. Research on the basic physics of systems generating optical coherence without lasing, may lead to new types of coherent light sources, new methods of light guiding, and new optical switching methods.
Coherent light is light that has no random "noise": you can think of a coherent light source as like the sound from a bell with a pure tone, while incoherent light has random noise, like the sound of a radio tuned to no radio station. Most people are familiar with lasers, which generate coherent light via a special process predicted by quantum mechanics. In the past few years, researchers at several labs around the world, including ours, have developed a new type of solid-state system which generates coherent light by an entirely different process. This method involves getting the electrons inside a solid to act coherently; the quantum mechanical wave nature of the electrons is used to make the electrons oscillate in phase together, and the radiation from these electrons leads to coherent light emission. This new method of generating coherent light has already been shown to be more efficient than regular lasing, and several other novel effects have been seen such as vortices of light. This project will study the basic physics of this fascinating new type of optical system, known as Bose-Einstein condensation of polaritons. Graduate students will be trained to use cutting-edge methods of optics with time resolution of less than a trillionth of a second, and they will work on new designs of these solid-state structures, which require structures with dimensions of a few nanometers, i.e., billionths of meters. This type of device may eventually be used in optical communications to switch light on and off in trillionths of seconds, to direct light into different communications channels on the same time scales, and to make efficient coherent light emitters.
