[lokimedes]

Quantum or not, any type of propagating and interacting particle or force can be used for communication. We primarily rely on electromagnetism but neutrinos, gravitational waves, charged or neutral particle beams etc. could be used as well. All of them have unique states that can be used to encode information. Spin, charge, neutrino flavor phases, etc.

As for entangled pairs, which I presume you imply by quantum communication, it really isn’t a hidden dimension with magical properties of superluminal communication, it just implies that two particles can have shared/correlated quantum states (assuming you can keep coherence). The coherence requirement basically means that the longer a particle is exposed to the normal world, the bigger the chances of some kind of stray interaction with other particles or forces, that will break entanglement. Further, for using this for anything, we’ll need to store the local particle for the duration of flight of the emitted one. That is also a technical problem of some magnitude if the distances are light years.

The short answer is that we don’t even come near to monitoring all “propagators” let alone all possible encoding schemes for these, for SETI.