On the dynamics of spinor condensates in microcavities

• Main Author: Kammann, Elena
• Other Authors: Lagoudakis, Pavlos
• Published: University of Southampton 2013
• Subjects: 621.3815; QC Physics
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.577260

Semiconductor microcavities offer the possibility to strongly confine light in a small cavity volume. Here the light interacts strongly with the electronic excitations of the quantum wells, which are embedded in the cavity, giving rise to a new kind of quasiparticle called exciton-polaritons or polaritons. These polaritons are the superposition of a photon and an exciton and inherit a light effective mass from the photon part and strong inter-particle interactions from the exciton part. Polaritons have extremely rich physics such as Bose-Einstein condensation (BEC) and super fluidity, to name a few. Thanks to their spin properties and fast dynamics polaritons could have potential applications in ultrafast optoelectronics such as optical switches. Under certain conditions the strong coupling does not sustain and the Eigenstates of the system change to the uncoupled cavity and exciton mode, which is called the weak coupling regime. In this thesis non-linear effects in the strong and in the weak coupling regime are investigated. In particular a crossover between a photon and a polariton laser is observed. Distribution functions and the dynamic behaviour of the long-range coherence confirms great similarities with BEC and exhibit the transition between two coherent states. Following these observations we study the spinor nature of polaritons and photons. In single shot experiments the spontaneous symmetry breaking at the phase transition to a coherent state was shown. In a nearly isotropic system the phase of the order parameter was chosen spontaneously and showed strong variations from shot to shot. This phenomenon which was once identified as the smoking gun for BEC was observed in a polariton and a photon laser. The spinor nature of polariton condensates was further exploited by studying the transport of spin by a propagating polariton condensate. Whilst travelling through the sample the spin experiences the optical spin-Hall effect and coherently precesses around an effective magnetic field. We observe up to four complete revolutions of the pseodospin around the effective magnetic field and the formation of a spin pattern that extends to 300 microns.