Quantum Telatar formula: fading quantum capacity of Haar-random multimode attenuators

arXiv:2611.14822v1 Announce Type: new Abstract: Cellular communication is done over an imperfectly predictable multimode environment, where the sender only knows about the distribution of possible intermode coupling and scattering a signal faces. It may thus seem surprising that such communication is efficient. Telatar proved that the sender's lack of exact knowledge about the channel, on average, does not significantly hinder multimode communication. As the number $N$ of modes increases at fixed signal-to-noise ratio, the average capacity of a classical multimode fading channel grows linearly in $N$, like that of $N$ decoupled single-mode channels.