Towards macroscopic quantum superpositions & Theory of knots of light

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To interface photons with solid-state devices, we investigated the coupling of optically active quantum dots with optical micro- and nano-cavities. Initial experimental progress have led to the unexpected observation of ultra low threshold lasing of a photonic crystal defect mode cavity embedded with only 1 to 3 InAs self-assembled quantum dots as gain medium. Photon correlation measurements confirmed the transition from a thermal light source to a coherent light source. We also report on micro-pillar cavities with integrated oxidation apertures and electronic gates that provide an 80MHz single photon source with controllable polarization. A second set of experiments will be addressed that has as long-term aim the transfer of a superposition of a photon propagating in two directions into a superposition of two center-of-mass motions of a tiny mirror that is placed in one path of the photon. A crucial part of the proposed experiment is an optical cavity with one end mirror as small as 20 µm in diameter attached to a high Q mechanical cantilever. Such a system has been achieved with an optical quality factor of 2,100 and a mechanical quality factor of 100,000. This provides an excellent interferometric measurement of the thermal motion of the micro-mechanical system. The thermal motion of the center-of-mass mode can be counter acted using a feedback circuit to modulate an additional optical force. Experimental results will be shown that demonstrate the optical cooling from room temperature to 135 mK.