  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.
