Relating quantum incoherence, entanglement and superluminal signalling

Abstract

Hereby we inspect two-partite entanglement using thought experiment that relates properties of incoherently mixed states to the impossibility of faster-than-light (FTL) signalling. We show that if there appears a way to distinguish ensembles of particles that are described by the same density matrix, but are generated using different pure states -properties of entanglement (namely, non-classical correlations) could be employed to create an FTL signalling device. We do not claim FTL signalling is possible, rather, we establish the logical connection between the aforementioned properties of current physical theory which has not so far been evident.

Searching for interstellar quantum communications

“…They can "set" particles in such a way that the other side can then make a measurement, and immediately obtain the information. This is unphysical because faster-than-light signalling results in causality violations which are impossible to accept (Eberhard & Ross 1989;Bassi & Ghirardi 2008;Ghirardi & Romano 2012;Filatov & Auzinsh 2020).…”