The recent state-of-the-art double-slit experiments with single electrons and single photons seem to emphasize a contradictable dilemma concerning the ontological physical reality in quantum physics. Because of the importance of this problem, we propose and perform another modified laser-beam asymmetrical double-slit experiment with a constraint of single-photon interference. In the results, a Feynman condition with a mobile closing mask allows assessing the complementary contributions of photons passing through one or another slit. Under the assumption of applicable self-interference, a ‘which-way’ phenomenon is observed quantitatively in the vicinity of the main minima with low-intense interference fringes, demonstrating a possible solution to this problem. The result would encourage similar asymmetrical double-slit experiments with truly single photons or single electrons for consistent and direct observation of the wave-particle duality.

The recent state-of-the-art double-slit experiments with single electrons and single photons seem to emphasize contradictable dilemma concerning the ontological physical reality in quantum physics. Because of the importance of this problem, we propose and perform another modified laser-beam asymmetrical double-slit experiment. In the results, a Feynman condition with closing mask allows to assess qualitatively the interference contributions of photons passing through one or another slit. Moreover, a definite "which-way" phenomenon has been identified with a high experimental confidence. This would be the simplest way without any disturbance of the photon beam to observe simultaneously both their path and momentum in consistency with the quantum statistical concept.