P. Michler

The emission of semiconductor quantum dots (QDs) has been shown to exhibit excellent properties in terms of single photon purity, photon indistinguishability and entanglement fidelity, i.e. essential prerequisites for quantum communication. Emission in the telecom O- or C-band will boost the range of communication schemes due to the favourable absorption and dispersion properties of silica fibers employed in the existing global fiber network. By metal-organic vapor-phase epitaxy, we have fabricated InAs quantum dots on InGaAs/GaAs metamorphic buffer layers on a GaAs substrate with area densities that allow addressing single quantum dots. The photoluminescence emission from the quantum dots is shifted to the telecom C-band at 1.55 μm with a high yield due to the reduced stress in the quantum dots. Single- and polarization-entangled photon emission is demonstrated. Furthermore, the coherence properties of photons emitted by InAs/InGaAs QDs emitting directly in the telecom C-band, are examined under above-band excitation and in resonance fluorescence. The average linewidth is reduced from 9.74 GHz in above-band excitation to 3.5 GHz in resonance fluorescence. Two-photon excitation of the biexciton is investigated as a resonant pumping scheme. A deconvoluted single-photon purity value of g(2)(0) = 0.07 and a postselected degree of indistinguishability of VHOM = 0.89 are determined for the biexciton transitions. Finally, to boost the extraction efficiency, the applicability of an approach combining a nano-membrane containing QDs, with a GaP hemispherical lens is presented for a sample emitting in the telecom O-band.