  Quantum superposition is the heart of quantum mechanics as mentioned by Dirac
and Feynman. In an interferometric system, single photon self-interference has
been intensively studied over the last several decades in both quantum and
classical regimes. In Born rule tests, the Sorkin parameter indicates the
maximum number of possible quantum superposition allowed to the input photons
entering an interferometer, where multi-photon interference fringe is
equivalent to that of a classical version by a laser. Here, an attenuated laser
light in a quantum regime is investigated for self-interference in a
Mach-Zehnder interferometer, and the results are compared with its classical
version. The resulting equivalent results support the Born rule tests, where
the classical interference originates in the superposition of individual
single-photon self-interferences. This understanding sheds light on the
fundamental physics of quantum features between bipartite systems.
