1Emission from a resonantly excited quantum emitter is a fascinating research topic within quantum optics and a useful source for different types of quantum light fields. The resonance spectrum consists of a single spectral line below saturation of a quantum emitter which develops into a triplet at powers above saturation of the emitter [1][2][3]. The spectral properties of the triplet strongly depends on pump power [4,5] and detuning of the excitation laser. The three closely spaced photon channels from the resonance fluorescence have different photon statistical signatures [6]. We present a detailed photon-statistics analysis of the resonance fluorescence emission triplet from a solid state-based artificial atom, i.e. a semiconductor quantum dot. The photon correlation measurements demonstrate both 'single' and 'heralded' photon emission from the Mollow triplet sidebands [6]. The ultra-bright and narrowband emission (5.9 MHz into the first lens) can be conveniently frequency-tuned by laser detuning over 15 times its linewidth (∆ν ≈ 1.0 GHz). These unique properties make the Mollow triplet sideband emission a valuable light source for, e.g.quantum light spectroscopy and quantum information applications [7].Generation of non-classical light fields like single-, entangled-and heralded-photons form a vital part of many schemes of quantum information and computation. Atom optics demonstrated the heralded emission of single photons using resonance fluorescence from single atoms [8] and from cold atoms in a cavity [9]. Currently most of the heralded photon schemes use sources based on parametric down conversion [10]. Recently, there has been important developments in fiber-based heralded photon sources using four-wave mixing [11].Both of these techniques present Poissonian statistics with photon bandwidths usually larger than 100 GHz. The increased two-photon yield in these photon sources is at the expense of fidelity. Semiconductor QDs have demonstrated single- [12], entangled- [13,14] and heralded-photon sources [15] but mostly under non-resonant excitation schemes. Though, coherent excitation conditions of those quantum emitters are an important precondition since these promise to minimize most of the dephasing caused by the non-resonant, i.e. incoherent processes [7]. Coherent control of QD excitons has been demonstrated in a variety of experiments exhibiting Rabi splitting [16], Rabi oscillations [17], and resonant absorption [18,19]. Observations of oscillations in the first-order correlation [20], charac-2 teristic emission spectra in the frequency domain [21], and oscillations of the second-order photon correlation function [2] were all measured directly on the resonance emission from the QD. In particular, single-photon emission from a single fluorescence line (below the emitter saturation) along with photon indistinguishability as high as 90% was demonstrated [3]. Also the AC Stark shift of an exciton was used to bring the initially split QD exciton components into resonance with each other, thus forming a ...

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

We demonstrate ultra-sensitive chemical sensing in the mid-infrared spectral regime with a combination of quantum cascade lasers (QCLs) with GaAs/Al(0.2)Ga(0.8)As strip waveguides fabricated via metal-organic vapor-phase epitaxy (MOVPE) and reactive ion etching (RIE) using evanescent field absorption spectroscopy. These strip waveguides have been designed with a width of 200 μm, thereby facilitating 2-D confinement and mode-matched propagation of mid-infrared radiation emitted from a distributed feedback (DFB) QCL at a wavelength of 10.3 μm. Acetic anhydride was detected with a limit of detection (LOD) of 18 pL (19.4 ng) deposited at the waveguide surface by overlapping of the vibrational absorption of the methyl group with the emission frequency of the QCL. The obtained results indicate a remarkable enhancement in sensitivity by three orders of magnitude compared to previously reported multimode planar silver halide waveguides. Further reduction of the waveguide strip width to 50 μm resulted in an additional sensitivity enhancement yielding a calculated LOD of 0.05 pL for the exemplary analyte acetic anhydride, which is among the most sensitive evanescent field absorption measurements with a miniaturized mid-infrared sensor system reported to date.

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.

The dark exciton state strongly affects the optical and quantum optical properties of flat InP/GaInP quantum dots. The exciton intensity drops sharply compared to the biexciton with rising pulsed laser excitation power while the opposite is true with temperature. Also, the decay rate is faster for the exciton than the biexciton and the dark-to-bright state spin flip is enhanced with temperature. Furthermore, long-lived dark state related memory effects are observed in second-order cross-correlation measurements between the exciton and biexciton and have been simulated using a rate-equation model.