  A recently proposed gedankenexperiment involving the (gravitational or
electromagnetic) interaction between two objects--one placed in a state of
quantum superposition of two locations--seems to allow for faster-than-light
communication. However, it has been argued that, if the mediating fields are
endowed with quantum properties, then the possibility for superluminal
signaling is fully avoided. Moreover, in the gravitational case, this
conclusion has been used to argue for the view that the gravitational field
must be quantized. In this work, we clarify and complement some aspects of the
discussion. In particular, by focusing on the way in which entanglement spreads
across the components of the system, we offer some insights into the
fundamental quantum features behind the impossibility of superluminal signaling
and we provide a more general proof of such an impossibility in this and
related protocols.
