Multiplexing is a strategy to augment the transmission capacity of a communication system. It consists of combining multiple signals over the same data channel and it has been very successful in classical communications. However, the use of enhanced channels has only reached limited practicality in quantum communications (QC) as it requires the manipulation of quantum systems of higher dimensions. Considerable effort is being made towards QC using high-dimensional quantum systems encoded into the transverse momentum of single photons, but so far no approach has been proven to be fully compatible with the existing telecommunication fibers. Here we overcome such a challenge and demonstrate a secure high-dimensional decoy-state quantum key distribution session over a 300-m-long multicore optical fiber. The high-dimensional quantum states are defined in terms of the transverse core modes available for the photon transmission over the fiber, and theoretical analyses show that positive secret key rates can be achieved through metropolitan distances.

We explore the propagation of the cylindrical vector beams (CVB) in turbid tissue-like scattering medium in comparison with the conventional Gaussian laser beam. The study of propagation of CVB and Gaussian laser beams in the medium is performed utilizing the unified electric field Monte Carlo model. The implemented Monte Carlo model is a part of a generalized on-line computational tool and utilizes parallel computing, executed on the NVIDIA Graphics Processing Units (GPUs) supporting Compute Unified Device Architecture (CUDA). Using extensive computational studies, we demonstrate that after propagation through the turbid tissue-like scattering medium, the degree of fringe contrast for CVB becomes at least twice higher in comparison to the conventional linearly polarized Gaussian beam. The results of simulations agree with the results of experimental studies. Both experimental and theoretical results suggest that there is a high potential of the application of CVB in the diagnosis of biological tissues.

In the current report, we present further developments of a unified open-access Monte Carlo (MC) based computational tool for simulation of twisted light propagation in turbid tissue-like scattering medium. We introduce an online browser-based application and a media model which considers both spatial and volumetric variations such surface roughness and subsurface scattering optical properties. The online application has been integrated with the parallel simulation framework developed in-house and is being extensively used in the ongoing studies of twisted light propagation in turbid media (e.g. phantoms and cancerous lesions). Rigorous validation against data obtained during experimental studies is presented.

We propose two experimental schemes for nanofiber-based compensated optical dipole traps that optimize the collective coupling of a one-dimensional array of atoms. The created array satisfies the second-order Bragg condition ($d=λ$), facilitating constructive interference of atomic radiation into the nanofiber and generating coherent back reflections of guided modes. Both schemes use far-off resonance light to minimize light scattering and atomic heating. Our numerical study focuses on $^{87}$Rb atoms. The results are generalizable to different atomic species and could improve the study of collective and nonlinear atomic effects.

We propose two experimental schemes for nanofiber-based compensated optical dipole traps that optimize the collective coupling of a one-dimensional array of atoms. The created array satisfies the second-order Bragg condition ( d = λ ), facilitating constructive interference of atomic radiation into the nanofiber and generating coherent back reflections of guided modes. Both schemes use far-off resonance light to minimize light scattering and atomic heating. Our numerical study focuses on the D2 line for 87 Rb atoms. The results are generalizable to different atomic species and could improve the study of collective and nonlinear atomic effects.

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