Very interesting, I studied telecommunications and I thought the Shannon limit was the absolute limit. I wonder now if this Gordon Holevo limit is applicable for "traditional" telecommunications (like 5G) as opposed to photon counting a deep space probe

EDIT: This paper seems to answer my question [1]

[1] https://opg.optica.org/directpdfaccess/8711ab35-bbc2-4d51-8e...