  Bipartite quantum interactions have applications in a number of different
areas of quantum physics, reaching from fundamental areas such as quantum
thermodynamics and the theory of quantum measurements to other applications
such as quantum computers, quantum key distribution, and other information
processing protocols. A particular aspect of the study of bipartite
interactions is concerned with the entanglement that can be created from such
interactions. In this Letter, we present our work on two basic building blocks
of bipartite quantum protocols, namely, the generation of maximally entangled
states and secret key via bipartite quantum interactions. In particular, we
provide a nontrivial, efficiently computable upper bound on the
positive-partial-transpose-assisted quantum capacity of a bipartite quantum
interaction. In addition, we provide an upper bound on the secret-key-agreement
capacity of a bipartite quantum interaction assisted by local operations and
classical communication. As an application, we introduce a cryptographic
protocol for the readout of a digital memory device that is secure against a
passive eavesdropper.
