Towards a loophole-free demonstration of EPR nonlocality

Abstract

This work reports on the progress in the experimental demonstration of steering as proposed by H. Wiseman and N. Brunner [11].<br />The term steering was originally proposed by E. Schrödinger in his response to the EPR paradox [2,7-9], but was only recently rigorously formalized in [10], where it was proven that Bell nonlocal states are a strict subset of EPR-steerable states which are in turn a strict subset of entangled states. Special emphasis in this work is set on the optimization of the coupling- or heralding efficiency of the Sagnac polarization entanglement source.<br />The coupling efficiency is a vital parameter in all applications of photonic entanglement sources, where low loss is of any importance, as it contributes to the single photon link efficiency and thus the total detection probability. It is also of great significance in attempts to experimentally refute notions of local realism, such as steering, since it results in the fair sampling loophole [19]. Therefore a measurement series of the single-mode coupling ratio in the degenerate collinear spontaneous parametric down-conversion process, under various focusing conditions, was conducted and analyzed.