  One of the most striking quantum phenomena is photon bunching resulting from
coincidently impinging two-indistinguishable photons on a beam splitter (BS)
from two different input ports. Such a nonclassical feature has also been
observed even between two independent light sources through either coherence
optics resulting in phase locking or post-selected measurements such as quantum
beating-based gating. Recently, BS physics regarding quantum features has been
discussed using pure coherence optics based on phase basis superposition of the
BS. Here, we experimentally demonstrate coherent photon bunching on a BS, where
coherent photons come from the same input port. Although the mean values of
both output photons are uniform and equal to each other, the mean value of the
coincidence measurements between two output photons results in the nonclassical
feature of photon bunching at a 50% rate. For this unprecedented result, we
discuss the origin of indistinguishability for this quantum feature using the
wave nature of a photon to understand the role of a BS in quantum mechanics.
