Progress towards a loophole-free test of nonlocality

We report on our progress towards a loophole-free test of nonlocality using spontaneous parametric down-conversion (SPDC). While the timing loophole can be easily closed in such a system by moving the detectors far apart [1], closing the detector loophole is significantly more difficult. In the standard Bell entangled states with the maximal violation of the CHSH inequality [2], an overall efficiency of 83\% is required. This limit can be lowered to 67\% by using non-maximally entangled states (although sensitivity to noise is greatly increased) [3]. We are carefully engineering our source to achieve maximal heralding efficiency, by optimizing both the spatial and spectral filtering, while keeping noise low using high-extinction-ratio polarizing beamsplitters. Combined with high-efficiency detectors, either optimized visible-light photon counters [4] or transition-edge sensors [5], closure of the detection loophole is within reach. \\[4pt] [1] G. Weihs et al., Phys. Rev. Lett. 81, 5039 (1998).\newline [2] J. F. Clauser et al., Phys. Rev. Lett. 23, 880 (1969).\newline [3] P.H. Eberhard, Phys. Rev. A 47, R747 (1993).\newline [4] S. Takeuchi et al., Appl. Phys. Lett. 74, 1063 (1999).\newline [5] A. E. Lita, A. J. Miller, and S. Nam, Opt. Exp. 16, 3032 (2008).