Recently, a laser beam asymmetrical double-slit experiment was proposed and performed, concerning ontological physical reality in quantum mechanics, under an assumption of single-photon interference. In the present study, by controlling better for saturation effects and upgrading the slit’s shape, we succeed in producing new interference samples with acceptable quality. Applying almost the same geometrical set-up, the present experiment makes the ”which-way” identification with higher experimental confidence. In the results, the ontological which-way effect observed in our recent experiment is well reconfirmed without any additional measurement of relative integral intensity.

The problem of physical reality in quantum mechanics has been raised since the famous Einstein-Bohr debate at the 5th Solvey conference in 1927. Ignoring the reality of a quantum matter existing independent of human observation, Bohr proposed an interpretation through the principle of complementarity, which negates simultaneous measurements of both characteristics of wave-particle duality. Until now, the issue remains unresolved and has received increasing attention over the past decade. Here we show for the first time a novel experimental correlation between two substitutionary which-way effects in asymmetrical double-slit experiments performed under the far-field Fraunhofer condition. The identifiable paired fringes can be seen in the self-interference spectra of single photons, travelling through different paths as point-like particles. The correlation greatly improves the confidence level and turns the present experiment into unambiguous evidence for the simultaneous measurement of wave-particle duality to the ontological physical reality of photons against the orthodox interpretation of quantum mechanics.