Max-Planck-AG Nichtklassische Strahlung, Humboldt University of Berlin, D-12484 Berlin, Germany.
Department of Mathematics, University of Zagreb, GF, Kaciceva 26, POB-217, HR-10001 Zagreb, Croatia; firstname.lastname@example.org; http://m3k.grad.hr/pavicic
Abstract. A method for preparing a loophole-free four-photon Bell experiments which requires a detection efficiency of 67% is proposed. It enables realistic detection efficiencies of 75% at a visibility of 85%. Two type-II crystals each down convert one correlated photon pair and we entangle one photon from one pair with one photon from the other pair on a highly transparent beam splitter. The entanglement selects two other conjugate photons into a Bell state. Wide solid angles for the conjugate photons then enable us to collect close to 100% of them. The cases when both photon pairs come from only one of the two crystals are successfully taken into account. Hardy's equalities are discussed.
PACS numbers: 42.50.Dv, 03.65.Bz.
Keywords: four photon interferometry, non-maximal singlet entaglement, quantum optics, quantum nonlocality, loophole-free Bell experiment, Hardy's inequality.