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Single photon sources (SPS) based on semiconductor quantum dot (QD) platforms are restricted to low temperature (T) operation due to the presence of strong dephasing processes. Despite the integration of QD in optical cavities provides an enhancement of its emission properties, the technical requirements for maintaining high indistinguishability (I) at high T are beyond the state of the art. Recently, new theoretical approaches have shown promising results by implementing two-dipole-coupled-emitter systems. Here, we have developed a theory to estimate I in a two-emitter system with strong dephasing coupled to a photonic cavity. We have obtained an analytical expression for I that predicts the cavity restrictions depending on the distance between the emitters. Furthermore, we develop an alternative interpretation of I which provide insigths for systems with a larger number of emitters. We find the optimal configuration for maximum I in the case of a five-emitter system using a machine-learning optimization procedure which models the Lindblad equation and provides the optimal position of each emitter to maximize I. The optimized configuration provides perfect I while relaxes the cavity requirements to more experimentally accessible values.

Room-temperature (RT), on-chip deterministic generation of indistinguishable photons coupled to photonic integrated circuits is key for quantum photonic applications. Nevertheless, high indistinguishability (I) at RT is difficult to obtain due to the intrinsic dephasing of most deterministic single-photon sources (SPS). Here we present a numerical demonstration of the design and optimization of a hybrid slot-Bragg nanophotonic cavity that achieves theoretical near-unity I and high coupling efficiency (\b{eta}) at RT for a variety of singlephoton emitters. Our numerical simulations predict modal volumes in the order of 10-3 ({\lambda}/2n)3 , allowing for strong coupling of quantum photonic emitters that can be heterogeneously integrated. We show that high I and \b{eta} should be possible by fine-tuning the quality factor (Q) depending on the intrinsic properties of the single-photon emitter. Furthermore, we perform a machine learning optimization based on the combination of a deep neural network and a genetic algorithm (GA) to further decrease the modal volume by almost three times while relaxing the tight dimensions of the slot width required for strong coupling. The optimized device has a slot width of 20 nm. The design requires fabrication resolution in the limit of the current state-ofthe-art technology. Also, the condition for high I and \b{eta} requires a positioning accuracy of the quantum emitter at the nanometer level. Although the proposal is not a scalable technology, it can be suitable for experimental demonstration of single photon operation

One of the main steps towards large-scale quantum photonics consists of the integration of single photon sources (SPS) with photonic integrated circuits (PICs). For that purpose, the PICs should offer an efficient light coupling and a high preservation of the indistinguishability of photons. Therefore, optimization of the indistinguishability through waveguide design is especially relevant. In this work we have developed an analytical model to calculate the coupling and the indistinguishability of an ideal point-source quantum emitter coupled to a photonic waveguide depending on source orientation and position. The model has been numerically evaluated through finite-difference time-domain (FDTD) simulations showing consistent results. The maximum coupling is achieved when the emitter is embedded in the center of the waveguide but somewhat surprisingly the maximum indistinguishability appears when the emitter is placed at the edge of the waveguide where the electric field is stronger due to the surface discontinuity.

We investigate how the voltage control of the exciton lateral dipole moment induces a transition from singly to doubly connected topology in type II InAs/GaAsSb quantum dots. The latter causes visible Aharonov-Bohm oscillations and a change of the exciton g-factor which are modulated by the applied bias. The results are explained in the frame of realistic $\mathbf{k}\cdot\mathbf{p}$ and effective Hamiltonian models and could open a venue for new spin quantum memories beyond the InAs/GaAs realm., Comment: Final Version

We propose type-II GaAsSb/GaAsN superlattices (SLs) lattice-matched to GaAs as a novel material for the 1 eV sub-cells present in highly efficient GaAs/Ge-based multi-junction solar cells. We demonstrate that, among other benefits, the spatial separation of Sb and N allows a better control over composition and lattice matching, avoiding the growth problems related to the concomitant presence of both elements in GaAsSbN layers. This approach not only reduces clustering and improves crystal quality and interface abruptness, but also allows for additional control of the effective bandgap in the 1.0-1.15 eV spectral region through the SL period thickness. The optimized SL structure exhibits a type-II band alignment and strong electronic coupling at 0 V. Both effects cooperate to increase the minority carrier collection and leads to a net strong enhancement of the external quantum efficiency (EQE) under photovoltaic conditions with respect to bulk layers of equivalent thickness., Comment: 21 pages, 6 figures, 4 supporting figures

Using the mechano-optical stress sensor technique, we observe a counter-intuitive reduction of the compressive stress when InAs is deposited on GaAs (001) during growth of quantum posts. Through modelling of the strain fields, we find that such anomalous behaviour can be related to the strain-driven detachment of In atoms from the crystal and their surface diffusion towards the self-assembled nanostructures., Comment: 10 pages, 4 figures. Published in APL Materials

In this work we use the in-situ accumulated stress monitoring technique to evaluate the evolution of the stress during the strain balancing of InAs/GaAs quantum dots and quantum posts. The comparison of these results with simulations and other strain balanced criteria commonly used indicate that it is necessary to consider the kinematics of the process, not only the nominal values for the deposited materials. We find that the substrate temperature plays a major role on the compensation process and it is necessary to take it into account in order to achieve the optimum compensation conditions. The application of the technique to quantum posts has allowed us to fabricate nanostructures of exceptional length (120 nm). In situ accumulated measurements show that, even in shorter nanostrcutures, relaxation processes can be inhibited with the resulting increase in the material quality., Comment: 6 pages, 6 figures. To be submitted to Physical Review B

Quantum posts are assembled by epitaxial growth of closely spaced quantum dot layers, modulating the composition of a semiconductor alloy, typically InGaAs. In contrast with most self-assembled nanostructures, the height of quantum posts can be controlled with nanometer precision, up to a maximum value limited by the accumulated stress due to the lattice mismatch. Here we present a strain compensation technique based on the controlled incorporation of phosphorous, which substantially increases the maximum attainable quantum post height. The luminescence from the resulting nanostructures presents giant linear polarization anisotropy., Comment: Submitted to Applied Physics Letters (7th March 2011). 4 pages, 4 figures