[cryptonector]

They are not, for the thing that would make neutrinos useful for communications is also the thing that makes them useless for communications. In order to use them for comms you'd need to produce such a huge number of neutrinos, and/or in a very colimated beam, that one shudders to think of how one might produce them!

[benlivengood]

I think you could moderate a large nuclear fission reactor (on the edge of criticality) to produce detectable differences in neutrino rate on the other side of the world. KamLAND and a few other experiments detected multi-GW reactor anti neutrinos at 1000km[0] and so presumably tens of GW (easily [if perhaps not safely?] achievable briefly in current reactors) should be detectable over 8000km.

[0] https://www.sciencedirect.com/science/article/pii/S173857331...

[Figs]

I suspect it may be possible using neutrino-antineutrino annihilation if there's a good way to produce streams of both types of particles, but... physics isn't my field.