  Photon statistics is one of the key properties of the photon state for the
study of quantum coherence and quantum information techniques. Here, we discuss
the photon indistinguishability induced bunching effect which can significantly
change photon statistics. Through the measurement of the second-order degree of
coherence of a mixed photon state composed of a single-photon state and a weak
coherent state, the statistical transition from a classical behavior to a
nonclassical behavior is experimentally demonstrated by modifying the
indistinguishability of the two-photon states. The study will help us to
understand and control the photon statistics with a method for quantum optical
coherence and quantum information applications. It also indicates that the
photon indistinguishability is a key parameter for multipartite quantum
coherence.
