Capacity Estimates for TRO Channels

Using the notion of TROu0027s (ternary ring of operators) and independence from operator algebra theory, we discover a new class of channels which allow single-letter bounds for their quantum and private capacity, as well as strong converse rates. This class goes beyond degradable channels. The estimate are based on a local comparison theorem for sandwiched Ru0027enyi relative entropy and complex interpolation. As an application, we discover new small dimensional examples which admit an easy formula for quantum and private capacities.