Reliability of the beam-splitter-based Bell-state measurement

An overview is given of the experimental evidence that a successful BSM cannot be claimed solely based on the coincidence data alone, because the interference features which are commonly considered as the signature of a successful BSM may, in fact, be obtained with input states incapable of violating a Bell inequality. Furthermore it is demonstrated that the conditions that lead to a positive result are indeed different than the conditions required of a polarization-entangled state or a proper Bell state projection.