Directly estimating the Holevo capacity of discrete Weyl channels

We propose a tight lower bound on the Holevo capacity of discrete Weyl channels (DWCs), which gives the exact Holevo capacity of known special cases of DWCs. Furthermore, for a physically available but otherwise unknown (channel parameters) DWC, this bound can be directly estimated by utilizing d + 1 measurement configurations without entanglement and joint measurements. We show that the performance of directly estimating the proposed bound is comparable with first performing the entanglement-based optimal parameter estimation of the DWC and then computing the proposed lower bound.