Nonclassical Behaviors of Two-Sender Multiple Access Channels

We take a device-independent approach to comparing the input-output correlations generated by quantum and classical multiple access channels (MACs). Classically, each sender transmits one bit to the receiver while an unlimited amount of shared randomness is held between devices. We derive a set of linear inequalities bounding the probability distributions accessible to classical MACs and use these inequalities to witness nonclassical behaviors. We consider two types of quantum MACs.  In the first, each sender transmits one qubit to the receiver, while in the second, the senders each transmit one classical bit and are assisted with shared entanglement. Using variational quantum optimization, we find maximally nonclassical behaviors for both types of quantum MAC. Both models are shown to violate the linear inequalities bounding classical MACs while entanglement-assisted MACs yield larger violations. Additionally, we identify fingerprinting as a task that shows no advantage when quantum communication is used, however, entanglement-assisted MACs demonstrate an advantage. Ultimately our results provide new insight into the role that distributed quantum resources can play in multi-party communication. 

Work funded by NSF award DMR-1747426