  The efficacies of maximally and that of non-maximally entangled mixed states
as teleportation channels have been studied. A new class of non-maximally
entangled mixed states have been proposed also. Their advantages as quantum
teleportation channels over existing non-maximally entangled mixed states have
been verified. The mixed states can also be generated using quantum cloning
machines. We have also studied how one can utilize the mixed entangled states
obtained as output from a state independent quantum cloning machine in
teleportation and dense coding. Mixed states can also be used in secret
sharing. A new protocol of secret sharing has been devised where four parties
are involved. One of them is honest by nature and the other is dishonest. The
dishonest one has two associates who are also involved in the protocol. It has
been shown how the honest party, by using quantum cloning machine, can prevent
the dishonest party from communicating the secret message to his accomplices. A
relation has been established among entanglement of the initially prepared
state, entanglement of the mixed state received by the recipients of the
dishonest one after honest party applies the cloning scheme and the cloning
parameters of the cloning machine. The usefulness of tri-partite and
four-partite entangled states in controlled dense coding has been discussed.
The thesis concludes with the summary and possible courses of future works.
