Fundamental Studies of Bose-Einstein Condensates of Polaritons

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Nontechnical Abstract:This project studies fundamental effects of quantum mechanics of optical states in semiconductor structures at low temperature. In particular, this project focuses on the process of Bose-Einstein condensation (BEC), in which many particles enter a single quantum state. The BEC studied here is comprised of “polaritons,” which can be viewed as photons with special properties; for example, they have mass and repel each other, like atoms. BEC has been studied extensively in gases of atoms at low temperature; this project on BEC of polaritons complements the study of BEC of atoms by providing new ways of looking at the system. In particular, the system under study in this project emits coherent light like a laser, which can be studied using advanced optical methods. The principle investigator (PI) of the project will also work closely with the Carnegie Science Center in Pittsburgh to present basic concepts of quantum mechanics to the public. Technical Abstract:This project builds on previous successful work on Bose-Einstein condensation of polaritons by pursuing three main goals: 1) Experiments at the University of Pittsburgh will aim at establishing the phase diagram of BEC under equilibrium conditions, including accurate determination of the condensate fraction as a function of density and temperature; 2) experiments at the University of Pittsburgh will study the onset of BEC from a “quench” (a highly nonequilibrium state) all the way to full equilibrium, in quasi-one-dimensional wires; and 3) experiments at the University of Pittsburgh will study macroscopic coherent states of a condensate in a circular ring, including spin texture and quantized angular momentum states. The above experiments involve ultrafast time-resolved optical spectroscopy, imaging, and interferometry methods available in the Snoke laboratories in Pittsburgh. For each of these thrusts, samples designed at the University of Pittsburgh are grown by molecular beam epitaxy at Princeton University and at the University of Waterloo, then delivered to Pittsburgh for final processing in the clean room at the University of Pittsburgh. This processing includes etching the structures to make one-dimensional wires for controlling the flow of the polariton condensate. The results of these experiments are studied in collaboration with a team of theorists from other universities including the University of Chicago, the University of Strathclyde, the University of Wolverhampton, and the University of Pittsburgh to address fundamental questions, such as the effect of interactions on depletion of the condensate, the theory of damping of a condensate out of equilibrium, and topologically nontrivial states of a condensate.This Division of Materials Research (DMR) grant supports research to understand the phase diagram of BEC under equilibrium and non-equilibrium conditions with funding from the Condensed Matter Physics (CMP) Program in DMR and the Atomic, Molecular and Optical Physics - Experiment (AMO-E) program in the Division of Physics (PHY) both of the Mathematical and Physical Sciences (MPS) Directorate.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.