Capacity of trace decreasing quantum operations and superadditivity of coherent information for a generalized erasure channel

Understand

Losses in quantum communication lines severely affect the rates of reliable information transmission and are usually considered to be state-independent.

• However, the loss probability does depend on the system state in general, with the polarization dependent losses being a prominent example.
• Here we analyze biased trace decreasing quantum operations that assign different loss probabilities to states and introduce the concept of a generalized erasure channel.
• We find lower and upper bounds for the classical and quantum capacities of the generalized erasure channel as well as characterize its degradability and antidegradability.