Information-theoretic aspects of the generalized amplitude damping channel

In this work, we provide an information-theoretic characterization and analysis of the generalized amplitude damping channel (GADC), which is the qubit analogue of the bosonic thermal loss channel. This channel can be used to model the disspation in a qubit system in the presence of an environment at a finite temperature, and it arises in the study of spin chains. The purpose of our work is to provide bounds on the fundamental limits of the GADC for communicating classical, quantum, and private information. Using the notion of approximate degradability, we provide upper bounds on the quantum and private capacities of this channel. We also provide upper bounds based on data processing inequalities by exploiting the mathematical decomposition of the GADC into channels for which the quantum capacity is known exactly. Using a similar decomposition technique, we are able to provide upper and lower bounds on the classical capacity of the GADC.