  Some modified two-slit interference experiments were carried out showing an
apparent paradox in wave-particle duality. In a typical such experiment, the
screen, where the interference pattern is supposed to be formed, is replaced by
a converging lens. The converging lens forms the images of the two slits at two
spatially separated detectors. It was claimed that each of these two detectors
give information about which slit a photon came from, even though they come
from the region of interference. These experiments generated a lot of debate.
The various refutations pointed out that the controversial claims involved some
questionable assumptions. However the refutations were largely philosophical in
nature, and one may like to substantiate those with arguments which are
testable, at least in principle. Here such an experiment is theoretically
analyzed by introducing path markers which are two orthogonal polarization
states of the photon. Analyzing the polarization at the two detectors shows
that the photons which give rise to interference, and reach a particular
detector, always come from both the slits. This provides clarity in
understanding such experiments by making use of testable quantum correlations.
