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

The influence of the bias voltage on emission properties of a red emitting InP/GaInP quantum dot based single-photon source was investigated. Under pulsed electrical excitation, we can influence the band bending of the p-i-n diode with the applied bias voltage and thus the charge carrier escape by quantum tunneling. This leads to control over the non-radiative decay channel and allows carrier escape times as low as 40 ps, effectively reducing the time jitter of the photon emission. We realized high excitation repetition rates of up to 2 GHz while autocorrelation measurements with g(2)(0)-values of 0.27 attest dominant single-photon emission.

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

We introduce a tomography approach to describe the optical response of a cavity quantum electrodynamics device, beyond the semiclassical image of polarization rotation, by analyzing the polarization density matrix of the reflected photons in the Poincaré sphere. Applying this approach to an electrically-controlled quantum dot-cavity device, we show that a single resonantly-excited quantum dot induces a large optical polarization rotation by 20 • in latitude and longitude in the Poincaré sphere, with a polarization purity remaining above 84%. The quantum dot resonance fluorescence is shown to contribute to the polarization rotation via its coherent part, whereas its incoherent part contributes to degrading the polarization purity.