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In this study, we have theoretically presented a prepare-and-measure based SARG04 protocol over free-space. It has been shown that the highest secret key rate is achievable even under free-space losses with a maximum noise tolerance.

An obvious way to entangle two atoms located at remote locations is to produce a pair of entangled photons half-way between the two atoms, to send one photon to each location and to subsequently map the photonic entanglement into the atoms. The efficiency of this process is, however, fundamentally limited due to overall transmission losses. We propose a method to herald the success of the mapping operation in free space without destroying nor revealing the stored quantum state. Interestingly for a Bell test, the heralding signal does not open the detection loophole provided the measurement choice is performed once the heralding is obtained only. We show through a detailed feasibility study that this approach could provide an attractive alternative to Bell tests where the atom–atom entanglement is created from atom–photon entanglement using an entanglement swapping operation.

We study modal characteristics of a customized ridge waveguide in lithium niobate designed to generate twin photons at telecom wavelength. A quantum analysis of SPDC predicts the possible down conversion processes and optimizes the input beam parameters for fundamental mode emission. Further, a joint spectral amplitude analysis ensures that the parameters are ambient for generating frequency-correlated photons throughout the phase-matching spectrum. Moreover, negatively correlated degenerate signal/idler photon pairs in the fundamental mode emission occurs at 1550 nm. A key result of our paper is an explicit expression and plot for comparing the generated signal power in case of waveguides as compared to bulk crystals. Our calculations clearly show a dependence of for a waveguide of length compared to a linear dependence in case of a bulk crystal. [ABSTRACT FROM AUTHOR]