Direct and reverse secret-key capacities of a quantum channel

We define the direct and reverse secret-key capacities of a memoryless quantum channel as the optimal rates that entanglement-based quantum key distribution protocols can reach by using a single forward classical communication (direct reconciliation) or a single feedback classical communication (reverse reconciliation). In particular, the reverse secret-key capacity is lower bounded by an additive quantity which is analytically computed for one-mode Gaussian channels.