Quantum information processing exploits the quantum nature of information. It offers fundamentally new solutions in the field of computer science and extends the possibilities to a level that cannot be imagined in classical communication systems. For quantum communication channels, many new capacity definitions were developed in comparison to classical counterparts. A quantum channel can be used to realize classical information transmission or to deliver quantum information, such as quantum entanglement. Here we review the properties of the quantum communication channel, the various capacity measures and the fundamental differences between the classical and quantum channels.

This paper is organized as follows. In Section II, preliminaries are summarized. In Section III, we study the classical information transmission capability of quantum channels. In Section IV, we discuss the quantum capacity. Numerical examples are included in Section V. Section VI focuses on the practical implementations of quantum channels. Finally, Section VII concludes the paper. Supplementary material is included in the Appendix.