  According to the identity principle in quantum theory, states of a system
consisted of identical particles should maintain unchanged under interchanging
between two of the particles. The whole wavefunction should be symmetrized or
antisymmetrized. This leads to statistical correlations between particles,
which exhibit observable effects. We design an experiment to directly observe
such effects for bosons. The experiment is performed with two photons. The
effect of statistical correlations is clearly observed when the wavepackets of
two photons are completely overlapped, and this effect varies with the degree
of overlapping. The results of our experiment substantiate the statistical
correlation in a simple way. Experiment reported here can also be regarded as
another kind of two-photon Hong-Ou-Mandel interference, occurs in the
polarization degree of freedom of photon.
