PROPOSAL FOR A LOOPHOLE-FREE BELL INEQUALITY EXPERIMENT

The nonlocality inherent in quantum mechanics has been tested experime ntally, but the nonlocal interpretation of all the relevant experiment s can be challenged. All past tests of Bell's inequalities have requir ed supplementary assumptions, without which the experimental results s atisfy the inequalities, in agreement with the notion of local realism . There are basically three loopholes that need to be closed; neither the cascade sources nor the parametric down-conversion sources of corr elation photons used to date are capable of closing all of them, even if the detectors used had been 100% efficient. We propose a two-crysta l down-conversion source, relying on type-II collinear phase matching, which should permit a violation of Bell's inequalities without the ne ed for supplementary assumptions. As the source can produce a true sin gletlike state, it is also relevant for quantum cryptographic applicat ions.