12:00 PM – 219 Allen Hall and Zoom

Ballistic Transport and Persistent Circulation of Exciton-Polariton Condensates

Bose-Einstein condensation (BEC) is a quantum macroscopic phenomenon and is closely related to superfluidity and superconductivity. In our lab, BEC is created at helium temperature (~10K) in semiconductors with excitonpolaritons (polaritons), a kind of quasi-particles which are superpositions of excitons and photons. In my PhD research, I mainly focused on creating persistent circulation out of polariton condensates in ring structures. In the first experiment, polariton condensate was injected at one point in a quasi-1D ring. Rather than observing the circulation, the condensates transported ballistically, and a clear precession of the polarization was seen, which arises from an effective spin-orbitcoupling term in the Hamiltonian. In the second experiment, we created a noncirculating condensate by using an optical trap and initiated the circulation in either direction on demand by a short laser pulse. The circulation persisted for at least 13ns, which is much longer than the polariton lifetime (~200ps) or the pulse duration (2ps). This experiment demonstrates the canonical effect of superfluidity and has potential applications for phase memory or optical qubits. In addition, I studied polariton condensate in wire structures and observed polariton drag effect, which is equivalent to changing light momentum with electric current.