Coherent free-space optical systems are limited by shot-noise which is essentially quantum limited. Similarly unrepeatered (links without amplification) links a

Coherent free-space optical systems are limited by shot-noise which is essentially quantum limited. Similarly unrepeatered (links without amplification) links are also shot-noise limited. So quantum limits are not really weird. Also the quantum limits can still be treated entirely classical, no need to think about "quantum weirdness"