## Subadditivity of the minimum output entropy and superactivation of the classical capacity of quantum multiple access channels

We study subadditivity of the minimum output entropy (H{sub min}) of quantum multiple access channels (MACs). We provide an example of violation of the additivity theorem for H{sub min} known in classical information theory. Our result is based on a fundamental property of MACs, i.e., independence of each sender. The channels used in the example can be constructed explicitly. On the basis of subadditivity of H{sub min} we also provide an example of extremal superadditivity (superactivation) of the classical capacity region of MACs.