Quantum networks could use spatial coherence instead of signal duplication

Angela Sara Cacciapuoti, Claudio Pellitteri, and Marcello Caleffi argue that spatial path superposition provides a no-cloning-compatible analogue of the spatial-diversity principle of MIMO. The researchers propose coherently delocalizing a quantum carrier across multiple communication links rather than duplicating it. This framework transforms the communication link into an integral part of quantum dynamics, potentially enhancing signal fidelity and even generating entanglement during transmission. A fundamental limitation of quantum communication, the no-cloning theorem, has long prevented direct application of classical techniques for improving signal reliability. Specifically, the classical Multi-Input Multi-Output (MIMO) spatial diversity, which uses multiple transmission paths for redundancy, is incompatible with quantum systems because it requires copying an unknown quantum state across independent links. Researchers are now proposing a method, spatial path superposition, that circumvents this restriction by exploiting quantum coherence rather than duplication. This approach allows a single quantum carrier to exist in a superposition of states propagating through multiple paths simultaneously, effectively integrating the communication link…