Exploiting Full Network Nonlocality From Quantum Key Distribution Perspective

Recently, the notion of full network nonlocality has emerged as some truly quantum network phenomena that cannot be realized in traditional Bell experiments. Present work manifests the utility of such form of truly network non-classicality in designing a four partite network-based entanglement assisted quantum key distribution protocol. Precisely, validity of the QKD protocol relies upon full network nonlocality detection via violation of some suitable trilocal inequality. Based on the quantum bit error rate and violation of trilocal inequality, arbitrary two qubit entangled states are characterized in accordance with their utility in successfully executing the protocol. The protocol is further analyzed from a restricted Eve-aware perspective by quantifying the Eve`s partial side information and discussing its implications for the corresponding Devetak-Winter 1-way secret key rate. Also, considering Eve's control over the trusted parties' measurement devices, an illustration of the protocol`s resistance to detection loophole is provided. Due to connected structure of entangled sources, any genuine form of network nonlocality may offer advantage over standard Bell nonlocality for designing secure key distribution protocols. To establish such an intuition as a fact, another QKD protocol, relying only upon Bell-CHSH violation, is designed. The former offers more stricter validity checks compared to the latter. Importantly, while the quantum bit error rate can be less than 14.6% exploiting Bell-CHSH nonlocality, it can be reduced below 13.7% by exploiting full network nonlocality.