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Single Semiconductor Quantum Dots in Microcavities: Bright sources of indistinguishable Photons

In this chapter we will discuss the technology and experimental techniques to realize quantum dot (QD) single photon sources combining high outcoupling efficiencies and highest degrees of non-postselected photon indistinguishability. The system, which is based on ultra low density InAs QDs embedded in a quasi planar single sided microcavity with natural photonic traps is an ideal testbed to study quantum light emission from single QDs. We will discuss the influence of the excitation conditions on the purity of the single photon emission, and in particular on the degree of indistinguishability of the emitted photons. While high purity triggered emission of single photons is observed under all tested excitation conditions, single photon interference effects can be almost vanish in experiments relying on non-resonant pumping into the quantum dot wetting layer. In contrast, we can observe nearly perfect indistinguishability of single photons in resonance fluorescence excitation conditions, which underlines the superiority of this excitation scheme to create photon wave packets close to the Fourier limit. As a first step towards the realization of solid state quantum networks based on quantum dot single photon sources we test the overlap of photons emitted from remote QDs yielding non-postselected interference visibilities on the order of ~40% for quasi resonant excitation.