Deterministic solid state quantum light sources are considered key building blocks for future communication networks. While several proof-of-principle experiments of quantum communication using such sources have been realized, most of them required large setups—often involving liquid helium infrastructure or bulky closed-cycle cryotechnology. In this work, we report on the first quantum key distribution (QKD) testbed using a compact benchtop quantum dot single-photon source operating at telecom wavelengths. The plug&play device emits single-photon pulses at O-band wavelengths (1321 nm) and is based on a directly fiber-pigtailed deterministically fabricated quantum dot device integrated into a compact Stirling cryocooler. The Stirling is housed in a 19 in. rack module including all accessories required for stand-alone operation. Implemented in a simple QKD testbed emulating the BB84 protocol with polarization coding, we achieve an multiphoton suppression of $g^{(2)}(0)=0.10\pm 0.01$ and a raw key rate of up to $(4.72\hspace{0.17em}\pm \hspace{0.17em}0.13)$ kHz using an external pump laser. In this setting, we further evaluate the performance of our source in terms of the quantum bit error ratios, secure key rates, and tolerable losses expected in full implementations of QKD while accounting for finite key size effects. Furthermore, we investigate the optimal settings for a two-dimensional temporal acceptance window applied on the receiver side, resulting in predicted tolerable losses up to 23.19 dB. Not least, we compare our results with previous proof-of-concept QKD experiments using quantum dot single-photon sources. Our study represents an important step forward in the development of fiber-based quantum-secured communication networks exploiting sub-Poissonian quantum light sources.

In this work, we demonstrate a triggered single-photon source operating at the telecom C-band with photon extraction efficiency exceeding any reported values in this range. The non-classical light emission with low probability of the multiphoton events is realized with single InAs quantum dots (QDs) grown by molecular beam epitaxy and embedded directly in an InP matrix. Low QD spatial density on the order of 5 × 10⁸ cm⁻² to ∼2 × 10⁹ cm⁻² and symmetric shape of these nanostructures together with spectral range of emission make them relevant for quantum communication applications. The engineering of extraction efficiency is realized by combining a bottom distributed Bragg reflector consisting of 25 pairs of InP/In_0.53Ga_0.37Al_0.1As layers and cylindrical photonic confinement structures. Realization of such a technologically non-demanding approach even in a non-deterministic fashion results in photon extraction efficiency of (13.3 ± 2) % into 0.4 numerical aperture detection optics at approximately 1560 nm emission wavelength, i.e., close to the center of the telecom C-band.

Solid‐state quantum light sources based on semiconductor quantum dots (QDs) are increasingly employed in photonic quantum information applications. Especially when moving towards real‐world scenarios outside shielded lab environments, the efficient and robust coupling of nanophotonic devices to single‐mode optical fibers offers substantial advantage by enabling “plug‐and‐play” operation. In this work we present a fiber‐pigtailed cavity‐enhanced source of flying qubits emitting single indistinguishable photons at clock‐rates exceeding 1 GHz. This is achieved by employing a fully deterministic technique for fiber‐pigtailing optimized QD‐devices based on hybrid circular Bragg grating (hCBG) micro‐cavities. The fabricated fiber‐pigtailed hCBGs feature emission lifetimes of ps, corresponding to a Purcell factor of ∼9, a suppression of multi‐photon emission events with g ⁽²⁾ (0) < 1 %, a photon‐indistinguishability % and a measured single‐photon coupling efficiency of 53 % in a high numerical aperture single‐mode fiber, corresponding to 1.2 Megaclicks per second at the single‐photon detectors under 80 MHz excitation clock‐rates. Furthermore, we show that high multi‐photon suppression and indistinguishability prevail for excitation clock‐rates exceeding 1 GHz. Our results show that Purcell‐enhanced fiber‐pigtailed quantum light sources based on hCBG cavities are a prime candidate for applications of quantum information science.

We demonstrate single-photon emission with a low probability of multiphoton events of 5% in the C-band of telecommunication spectral range of standard silica fibers from molecular beam epitaxy grown (100)-GaAs-based structure with InAs quantum dots (QDs) on a metamorphic buffer layer. For this purpose, we propose and implement graded In content digitally alloyed InGaAs metamorphic buffer layer with maximal In content of 42% and GaAs/AlAs distributed Bragg reflector underneath to enhance the extraction efficiency of QD emission. The fundamental limit of the emission rate for the investigated structures is 0.5 GHz based on an emission lifetime of 1.95 ns determined from time-resolved photoluminescence. We prove the relevance of a proposed technology platform for the realization of non-classical light sources in the context of fiber-based quantum communication applications.

Optical properties of molecular beam epitaxially grown type II “W” shaped GaSb/AlSb/InAs/GaIn(As)Sb/InAs/AlSb/GaSb quantum wells (QWs) designed for the active region of interband cascade lasers have been investigated. Temperature dependence of Fourier-transformed photoluminescence and photoreflectance was employed to probe the effects of addition of arsenic into the original ternary valence band well of GaInSb. It is revealed that adding arsenic provides an additional degree of freedom in terms of band alignment and strain tailoring and allows enhancing the oscillator strength of the active type II transition. On the other hand, however, arsenic incorporation apparently also affects the structural and optical material quality via generating carrier trapping states at the interfaces, which can deteriorate the radiative efficiency. These have been evidenced in several spectroscopic features and are also confirmed by cross-sectional transmission electron microscopy images. While arsenic incorporation into type II QWs is a powerful heterostructure engineering tool for optoelectronic devices, a compromise has to be found between ideal band structure properties and high quality morphological properties.