POSTSELECTION-FREE ENERGY-TIME ENTANGLEMENT

We report a two-photon interference experiment that realizes a postsel ection-free test of Bell's inequality based on energy-time entanglemen t. In contrast with all previous experiments of this type, the employe d entangled states are obtained without the use of a beam splitter or a short coincidence window to ''throw away'' unwanted amplitudes. A (9 5.0+/-1.4)% interference fringe visibility is observed, implying a str ong violation of the Bell inequality. The scheme is very compact and h as demonstrated excellent stability, suggesting that it may be useful, for example, in practical quantum cryptography.