Superadditivity of quantum channel coding rate with finite blocklength quantum measurements

This paper investigates the superadditivity of the maximum achievable information rate in a quantum channel. The superadditivity is a phenomenon that the maximum accessible information per channel strictly increases as the number of quantum states jointly measured increases. We give an explanation of this phenomenon by comparing the quantum channel with the classical discrete memoryless channel (DMC) under the concatenated codes, and give a lower bound on the maximum accessible information per channel at a finite length of quantum measurements in terms of V , which is the quantum version of channel dispersion, and C, the capacity of the quantum channel.