Quantum Photon Fluids in Flatland
- Chih-Wei Lai, MSU PA
Thursday, April 3, 4:10 PM - Physics and Astronomy Colloquium
Biomedical & Physical Sciences Bldg., Rm. 1415
Technological advances in fabricating optical cavities and quantum heterostructures at the nanoscale have allowed us to hybridize electronic excitations with photons in studies on macroscopic quantum states and emergent non-equilibrium phenomena in condensed matter. Optical excitations in a semiconductor microcavity lead to a 2D coupled electron-hole-photon (e-h-photon) system, in which BCS-BEC (Bardeen-Cooper-Schrieffer superconductor-Bose-Einstein condensate) crossover physics can be studied with varying particle densities and particle-particle interactions. In the BEC-like regime, a light-mass composite boson formed by admixing of photons with dipole-active excitations of the medium called a polariton comprises the basics for recent experiments on a high-temperature dynamic condensate. The Coulomb many-body interactions in polaritons lead to the formation of a dynamic macroscopically coherent polariton state that exhibit phenomena analogous to a Bose-Einstein condensate or superfluid, such as macroscopic occupation of polaritons in energy and momentum space, long-range spatial coherence, and vortices. In the BCS-like regime, light-induced e-h pairs are theoretically predicted to form and lead to a superfluid-like state. Experimentally, a spin-dependent multicomponent condensate of exciton-polaritons has not been much explored. We present our studies of a spin-polarized polariton state at high densities in a semiconductor microcavity both at room temperature and cryogenic temperatures. Our results not only can stimulate activities to exploit spin and many-body effects for fundamental studies of quantum light-matter fluids, but also facilitate developments of spin-dependent optoelectronic devices. We also discuss experimental aspects in addressing the BEC-BCS-lasing crossover problem in a 2D coupled e-h-photon system.