The role of resonant pumping schemes in improving the photon coherence is investigated on InAs/InGaAs/GaAs quantum dots (QDs) emitting in the telecom C-band. The linewidths of transitions of multiple exemplary quantum dots are determined under above-band pumping and resonance fluorescence (RF) via Fourier-transform spectroscopy and resonance scans, respectively. The average linewidth is reduced from (9.74 ± 3.3) GHz in the above-band excitation to (3.50 ± 0.39) GHz under RF underlining its superior coherence properties. Furthermore, the feasibility of coherent state preparation with a fidelity of (49.2 ± 5.8)% is demonstrated, constituting a first step toward on-demand generation of coherent, single, telecom C-band photons directly emitted by QDs. Finally, two-photon excitation of the biexciton is investigated as a resonant pumping scheme. A deconvoluted single-photon purity value of gHBT(2)(0)=0.072 ± 0.104 and a postselected degree of indistinguishability of VHOM=0.894 ± 0.109 are determined for the biexciton transition. This represents another step in demonstrating the necessary quantum optical properties for prospective applications.
Semiconductor quantum dots emitting in the telecommunication O- and C-bands are promising candidates as single-photon sources for fiber-based quantum communication. In this work, we show how coherent quasi-resonant and phonon-assisted excitation help reveal the intrinsic optical properties of InAs quantum dots embedded in relaxed InGaAs matrices on top of metamorphic InGaAs layers for achieving emission in the telecom bands. By systematically comparing excitation schemes, we separate excitation-induced effects from intrinsic emitter properties. This allows us to observe linewidths as narrow as 21
μeV, the disappearance of slow decay channels, and single-photon purity reaching second-order autocorrelation values in the order of
10−2. Photoluminescence excitation reveals higher excited states, enabling coherent control of trion transitions and the observation of Rabi-like oscillations in both telecom bands. These results confirm the promising potential of these quantum dots for applications in quantum technologies.
The goal of this Special Topic is to provide new insights in the physics of single quantum emitters and single-photon detectors and their possible use for quantum photonic applications. The perspective article of Vural and others discusses the challenges for multi-source quantum implementations based on self-assembled InGaAs quantum dots. Decoherence and spectral diffusion processes in quantum dots, which limit the photon indistinguishability, are considered in their article. In their article, Anderson and others have investigated the noise sources that affect InAs/InP quantum dots emitting in the telecom C-band by comparing their behavior on a wetting layer for Stranski-Krastanov grown quantum dots with a nearly wetting layer-free environment achieved with the droplet epitaxy growth mode. They show that the droplet epitaxy growth mode is beneficial for a low-noise environment, which is a pre-condition for the generation of highly coherent photons.