  The aim of this thesis is to advance the theory behind quantum information
processing tasks, by deriving fundamental limits on bipartite quantum
interactions and dynamics, which corresponds to an underlying Hamiltonian that
governs the physical transformation of a two-body open quantum system. The goal
is to determine entangling abilities of such arbitrary bipartite quantum
interactions. Doing so provides fundamental limitations on information
processing tasks, including entanglement distillation and secret key
generation, over a bipartite quantum network. We also discuss limitations on
the entropy change and its rate for dynamics of an open quantum system weakly
interacting with the bath. We introduce a measure of non-unitarity to
characterize the deviation of a doubly stochastic quantum process from a
noiseless evolution.
  Next, we introduce information processing tasks for secure read-out of
digital information encoded in read-only memory devices against adversaries of
varying capabilities. The task of reading a memory device involves the
identification of an interaction process between probe system, which is in
known state, and the memory device. Essentially, the information is stored in
the choice of channels, which are noisy quantum processes in general and are
chosen from a publicly known set. Hence, it becomes pertinent to securely read
memory devices against scrutiny of an adversary. In particular, for a secure
read-out task called private reading when a reader is under surveillance of a
passive eavesdropper, we have determined upper bounds on its performance. We do
so by leveraging the fact that private reading of digital information stored in
a memory device can be understood as secret key agreement via a specific kind
of bipartite quantum interaction.
