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Interaction of light with solid-state condensates

Quantum physics of light and of solid-state condensates such as superconductivity have been investigated extensively in separate fields of physics. Recently, novel collective phenomena have been demonstrated resulting from the combinations of solid-state systems with light. We study two such combinations: optoelectronic devices based on superconductor–semiconductor junctions, and semiconductor exciton-polariton condensates.

Superconductor-semiconductor junctions with low-Tc materials have been demonstrated recently to exhibit enhanced light emission. We show theoretically that superconductor-semiconductor devices result in emission of entangled photon pairs when a proximity layer is induced in the semiconductor nanostructures. We have developed a mechanical bonding technique enabling the fabrication of high-Tc superconductor–semiconductor junctions, and demonstrated experimentally a tunnel diode based on BSCCO/GaAs structures. Using this technique we also demonstrate proximity-induced high-Tc superconductivity in graphite and in candidate topological insulators Bi 2 Se 3 and Bi 2 Te 3 .

Exciton-polaritons that emerge from the strong coupling of photons to excitons in a high-quality semiconductor microcavity have an extremely small effective mass, and can therefore condense at very high temperatures. Spatial polariton BEC interferometry experiments have been done recently employing particle density induced potentials.  We experimentally demonstrate interference of polariton condensates resonantly injected at different times. This observation provides a direct measurement of the condensate temporal coherence. We also propose a more dynamic approach to generating potentials for polariton BEC by employing the optical Stark effect – similar to methods used in cold-atom systems. We show the first observation of the optical Stark shift of a strongly coupled light matter system with the special properties such as the dependence of the shift on the excitonic and the photonic nature of the polaritons.