  Bell states form a complete set of four maximally polarization entangled
two-qubit quantum state. Being a key ingredient of many quantum applications
such as entanglement based quantum key distribution protocols, superdense
coding, quantum teleportation, entanglement swapping etc, Bell states have to
be prepared and measured. Spontaneous parametric down conversion is the easiest
way of preparing Bell states and a desired Bell state can be prepared from any
entangled photon pair through single-qubit logic gates. In this paper, we
present the generation of complete set of Bell states, only by using unitary
transformations of half-wave plate (HWP). The initial entangled state is
prepared using a combination of a nonlinear crystal and a beam-splitter (BS)
and the rest of the Bell states are created by applying single-qubit logic
gates on the entangled photon pairs using HWPs. Our results can be useful in
many quantum applications, especially in superdense coding where control over
basis of maximally entangled state is required.
