Capacity Estimates via Comparison with TRO Channels

A ternary ring of operators (TRO) in finite dimensions is an operator space as an orthogonal sum of rectangular matrices. TROs correspond to quantum channels that are diagonal sums of partial traces, we call TRO channels. TRO channels have simple, single-letter entropy expressions for quantum, private, and classical capacity. Using operator space and interpolation techniques,we perturbatively estimate capacities, capacity regions, and strong converse rates for a wider class of quantum channels by comparison to TRO channels.