We report on pure-quantum-state polariton condensates in optical annular traps. The study of the underlying mechanism reveals that the polariton wavefunction always coalesces in a single pure-quantum-state that, counter-intuitively, is always the upp
ermost confined state with the highest overlap to the exciton reservoir. The tunability of such states combined with the short polariton lifetime allows for ultrafast transitions between coherent mesoscopic wavefunctions of distinctly different symmetries rendering optically confined polariton condensates a promising platform for applications such as many-body quantum circuitry and continuous-variable quantum processing.
We demonstrate experimentally the condensation of exciton-polaritons through optical trapping. The non-resonant pump profile is shaped into a ring and projected to a high quality factor microcavity where it forms a 2D repulsive optical potential orig
inating from the interactions of polaritons with the excitonic reservoir. Increasing the population of particles in the trap eventually leads to the emergence of a confined polariton condensate that is spatially decoupled from the decoherence inducing reservoir, before any build up of coherence on the excitation region. In a reference experiment, where the trapping mechanism is switched off by changing the excitation intensity profile, polariton condensation takes place for excitation densities more than two times higher and the resulting condensate is subject to a much stronger dephasing and depletion processes.
Periodic incorporation of quantum wells inside a one--dimensional Bragg structure is shown to enhance coherent coupling of excitons to the electromagnetic Bloch waves. We demonstrate strong coupling of quantum well excitons to photonic crystal Bragg
modes at the edge of the photonic bandgap, which gives rise to mixed Bragg polariton eigenstates. The resulting Bragg polariton branches are in good agreement with the theory and allow demonstration of Bragg polariton parametric amplification.
