  Light's wave-particle duality is at the heart of quantum mechanics and can be
well illustrated by Wheeler's delayed-choice experiment. The choice of
inserting or removing the second classical (quantum) beam splitter in a
Mach-Zehnder interferometer determines the classical (quantum) wave-particle
behaviors of a photon. In this paper, we report our experiment using the
classical beam splitter to observe the simultaneous wave-particle behaviors in
the wave-packet of a narrowband single photon. This observation suggests that
it is necessary to generalize the current quantum wave-particle duality theory.
Our experiment demonstrates that the produced wave-particle state can be
considered an additional degree of freedom and can be utilized in encoding
quantum information.
