Quantum properties of polariton condensates in microcavity devices

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Semiconductor microcavities (MC) are Fabry-Perot resonators which consist of high reflectivity mirrors and which contain embedded quantum wells in the active region. They enable both exciton and photon confinement in one direction. Strong exciton-photon coupling in these structures results in the formation of a new class of bosonic quasiparticles, described in terms of two-dimensional polaritons or mixed exciton photon states. Microcavity polaritons have favourable characteristics for the study of condensation phenomena and novel many body effects such as superfluidity in a solid-state system, which can be achieved at much higher temperature than that required for excitons and atoms due to their very small effective mass. An additional advantage of MC structures is that precise manipulation of the polariton states can be performed on a micrometer scale by an external laser field. In addition, strong polariton-polariton interactions enable the generation of non-classical states of photons. Also the internal structure of polariton states can be easily modified by the appropriate design of MC structures with resultant zero- or one- dimensional confinement. The key aim of my proposal will be accurately prepared macroscopically occupied high density polariton states with precise phase information and control of their polarisation and statistical properties. In order to prove the analogy with atomic condensates, but in a solid state system, one of the important parts of my proposal is dedicated to the study of spatial and temporal coherence of two interacting polariton condensates. Specially designed zero-dimensional photonic structures will also permit control of quantum fluctuations, which affect the coherence. Efficient generation of non-classical states of photons, squeezed light with polarisation selective control will be achieved using resonant excitation of the polariton ground states. Polaritonic states will be controlled by external applied uniaxial strain and applied magnetic field to achieve desired spin properties of polaritons and hence the polarisation of the polariton condensate. The proposed research will also focus on the study of interactions between the high density polariton phase and acoustic phonons, which will be important to understand new phenomena arising from condensation in the periodic potential induced by surface acoustic waves. Finally, the effects of squeezing and coherence properties of the polariton condensate will be investigated in wide band microcavities. The research is expected to lay a strong foundation for the future use of microcavity structures in quantum information technology and for the development of novel light sources, mixers and tunable optical filters.