It is commonly assumed that the observation of an interference pattern is incompatible with any information about the path taken by a quantum particle. Here we show that this assumption is contradicted by theoretically predicted experimental observations. A precise evaluation of the effects of sufficiently small polarization rotations in the slits of a double slit experiment indicates that the particles forming the interference pattern must have been physically delocalized, such that particles detected in the interference maxima have a presence of exactly one half in each slit while particles detected close to the minima appear to have a negative presence in one of the slits and a presence of more than one in the other.

It is commonly assumed that interference patterns contain no information about the path taken by the individual photons. Surprisingly, recent results based on the analysis of weak interactions with probe qubits suggest that this may be a misconception. Here we show that the fluctuations of detection events in quantum interference patterns are correlated with the fluctuations of particle presence in the paths. It is pointed out that this correlation is a general feature of quantum fluctuations that distinguishes them from classical noise.