F. De Martini, G. Denardo, and Y. Shih (eds.), Quantum Interferometry, (VCH Publishing Division I, New York, 1996), pp. 193-204.


Mladen Pavicic

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; mpavicic@faust.irb.hr; http://m3k.grad.hr/pavicic

Abstract. We present several kinds of experiments which prepare entanglements between photons that nowhere interacted and whose paths nowhere crossed. The experiments put together two or more photons from two or more (non-maximal) singlet-like or triplet-like photon pairs and make them interfere in the intensity at an asymmetrical beam splitter. As a result one finds polarization correlations between the other companion photons from the pairs whose paths nowhere crossed each other even when no polarization measurements have been carried out on the former photons upon emergence from the beam splitter. It turns out that the latter set of photons that nowhere interacted contains subsets of photons in the (non-maximal) singlet state and since we are able to extract such photons with probability one, we can consider them event-ready prepared in an entangled state by their pair-companion photons that interfered at the beam splitter. The preparation of photon pairs by beam splitters fed from nonlinear crystals as well as by single non-linear crystals of type-II are considered in realistic experimental conditions. Such setups can be used for closing all the remaining loopholes in the Bell theorem with detection efficiency as low as 67\%. One can do this with or without use of the Bell inequalities depending on the chosen orientations of the polarizers used in the experiments. The result reveals nonlocality as a property of selection which can even be a preselection. It also reveals that one can predict spin-correlated behaviour of photons in space and at beam splitters by controlling other than spin observables. On the other hand, the setup can be used for preparing non-maximal entangled states without losing counts as opposed to the attenuation method. [Abstract as appeared in the Book of Abstracts at the Workshop.]

PACS numbers: 03.65.Bz, 42.50.Wm

Keywords: four photon interferometry, asymmetrical beam splitters, non-maximal singlet correlation, quantum optics, quantum nonlocality, quantum teleportation, loophole-free Bell experiment.