  Quantum mechanics put restriction on performing some task which we can do
classically. One such restriction is that we cannot copy an arbitrary quantum
state. This is known as No-cloning theorem. Although quantum mechanics forbid
us to construct a perfect cloner, there is no restriction to construct an
imperfect cloner. Therefore, we have constructed and studied a special kind of
quantum cloning machine named as Hybrid quantum cloning machine which is
nothing but a different combination of pre-existing quantum cloning machines.
We showed that this hybrid quantum cloning machine sometime gives better
quality copy than the pre-existing quantum cloners. Quantum entanglement is a
very astonishing property in a multi-partite system and it is a very useful
ingredient of quantum information theory. Therefore broadcasting (cloning) of
entanglement is a very important subject to study. In this regard we have
studied the broadcasting of entanglement using state dependent quantum cloning
machine. Further, we have investigated the problem of secretly broadcasting of
three-qubit entangled state between two distant partners. Linearity of quantum
mechanics put another restriction on deletion of an arbitrary quantum state
i.e. an arbitrary quantum state against a copy cannot be perfectly deleted.
Like cloning machine one can construct an approximate deletion machine also.
Therefore, we have constructed an universal deletion machine in the sense that
the fidelity of deletion does not depend on the input state and showed that the
fidelity of deletion is 3/4 . Further we showed that the fidelity of deletion
depends on the blank state at the output and it can be improved from the value
3/4 for certain blank state. Moreover, we have studied the case where two
cloned copies are given at the input of the deletion machine.
