Super-additivity of quantum capacity in simple channels

TL;DR

This paper investigates the super-additivity of quantum capacity in simple channels, introducing a generalized platypus channel that exhibits super-additivity and has computable capacities, advancing understanding of quantum information transmission.

Contribution

It introduces the generalized platypus channel, proves its capacities are computable, and demonstrates its super-additivity with other quantum channels, extending prior work on quantum channel capacities.

Findings

Generalized platypus channel has capacity equal to 1 for private and classical capacities.

The channel exhibits super-additivity of quantum capacity with erasure and amplitude damping channels.

Capacities of the generalized platypus channel are explicitly computed and analyzed.

Abstract

The super-additivity of quantum channel capacity is an important feature of quantum information theory different from classical theory, which has been attracting attention. Recently a special channel called ``platypus channel'' exhibits super-additive quantum capacity when combined with qudit erasure channels. Here we consider the ``generalized platypus channel'', prove that it has computable channel capacities, such as both private and classical capacity equal to $1$, and in particular, the generalized platypus channel still displays the super-additivity of quantum capacity when combined with qudit erasure channels and multilevel amplitude damping channels respectively.