We demonstrate efficient (>30%) quantum frequency conversion of visible single photons (711 nm) emitted by a quantum dot to a telecom wavelength (1313 nm). Analysis of the first- and second-order coherence before and after wavelength conversion clearly proves that pivotal properties, such as the coherence time and photon antibunching, are fully conserved during the frequency translation process. Our findings underline the great potential of single photon sources on demand in combination with quantum frequency conversion as a promising technique that may pave the way for a number of new applications in quantum technology.

Abstract. We report on in-lab free space quantum key distribution (QKD) experiments over 40 cm distance using highly efficient electrically driven quantum dot single-photon sources emitting in the red as well as near-infrared spectral range. In the case of infrared emitting devices, we achieve sifted key rates of 27.2 kbit s −1 (35.4 kbit s −1 ) at a quantum bit error rate (QBER) of 3.9% (3.8%) and a g (2) (0) value of 0.35 (0.49) at moderate (high) excitation. (2) (0) value of 0.49. This first successful proof of principle QKD experiment based on electrically operated semiconductor single-photon sources can be considered as a major step toward practical and efficient quantum cryptography scenarios. Contents

Within this work we present optical and structural properties of InP quantum dots embedded in ͑Al x Ga 1−x ͒ 0.51 In 0.49 P barriers. Atomic force microscopy measurements show a mainly bimodal height distribution with aspect ratios ͑ratio of width to height͒ of about 10:1 and quantum dot heights of around 2 nm for the smaller quantum dot class ͑type A͒ and around 4 nm for the larger quantum dot class ͑type B͒. From ensemblephotoluminescence measurements we estimated thermal activation energies of up to 270 meV for the type-A quantum dots, resulting in a 300 times higher luminescence intensity at 200 K in comparison to our InP quantum dots in Ga 0.51 In 0.49 P at the same emission wavelength. Photon statistic measurements clearly display that InP quantum dots in ͑Al 0.20 Ga 0.80 ͒ 0.51 In 0.49 P emit single photons up to 80 K, making them promising candidates for high-temperature single-photon emitters.

We present an electrically pumped single-photon emitter in the visible spectral range, working up to 80 K, realized using a self-assembled single InP quantum dot. We confirm that the electroluminescense is emitted from a single quantum dot by performing second-order autocorrelation measurements and show that the deviation from perfect single-photon emission is entirely related to detector limitations and background signal. Emission from both neutral and charged exciton complexes was observed with their relative intensites depending on the injection current and temperature.

Electrically driven quantum dot single-photon source at 2GHz excitation repetition rate with ultra-low emission time jitter Appl. Phys. Lett. 102, 011126 (2013); 10.1063/1.4774392Triggered single-photon emission in the red spectral range from optically excited InP/(Al,Ga)InP quantum dots embedded in micropillars up to 100 K

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Single lateral InGaAs quantum dot molecules have been embedded in a planar micro-cavity in order to increase the luminescence extraction efficiency. Using a combination of metal-organic vapor phase and molecular beam epitaxy samples could be produced that exhibit a 30 times enhanced single-photon emission rate. We also show that the single-photon emission is fully switchable between two different molecular excitonic recombination energies by applying a lateral electric field. Furthermore, the presence of a polarization fine-structure splitting of the molecular neutral excitonic states is reported which leads to two polarization-split classically correlated biexcitonexciton cascades. The fine-structure splitting is found to be on the order of 10 µeV.