  The effect of noise on various protocols of secure quantum communication has
been studied. Specifically, we have investigated the effect of amplitude
damping, phase damping, squeezed generalized amplitude damping, Pauli type as
well as various collective noise models on the protocols of quantum key
distribution, quantum key agreement,quantum secure direct quantum communication
and quantum dialogue. From each type of protocol of secure quantum
communication, we have chosen two protocols for our comparative study; one
based on single qubit states and the other one on entangled states. The
comparative study reported here has revealed that single-qubit-based schemes
are generally found to perform better in the presence of amplitude damping,
phase damping, squeezed generalized amplitude damping noises, while
entanglement-based protocols turn out to be preferable in the presence of
collective noises. It is also observed that the effect of noise entirely
depends upon the number of rounds of quantum communication involved in a scheme
of quantum communication. Further, it is observed that squeezing, a completely
quantum mechanical resource present in the squeezed generalized amplitude
channel, can be used in a beneficial way as it may yield higher fidelity
compared to the corresponding zero squeezing case.
