Violation of Bell's inequality has been the mainspring for secure key generation in an entanglement assisted Quantum Key Distribution(QKD) protocol. Various contributions have relied on the violation of appropriate Bell inequalities to build an appropriate QKD protocol. Residing between Bell nonlocality and entanglement, there exist a hybrid trait of correlations, namely correlations exhibited through the violation of steering inequalities.However, such correlations have not been put to use in QKD protocols as much as their stronger counterpart, the Bell violations.In the present work, we show that the violations of the CJWR(E.G.Cavalcanti,S.J. Jones,H.M Wiseman and M.D. Reid, Phys.Rev.A 80,032112( 2009))steering inequalities can act as key ingredients in an entanglement assisted QKD protocol.We work with arbitrary two qubit entangled states, characterize them in accordance with their utility in such protocols. The characterization is based on the quantum bit error rate and violation of a CJWR inequality. Furthermore, we show that subsequent applications of local filtering operations on initially entangled states exhibiting non violation, lead to violations necessary for the successful implementation of the protocol. An additional vindication of our protocol is provided by the use of absolutely Bell-CHSH local states, states which remain Bell-CHSH local even under global unitary operations.

We study here a hitherto unexplored line of research, namely an investigation which reveals hidden nonlocality in a linear network with independent sources. In the usual paradigm of Bell nonlocality, there are certain states which exhibit nonlocality only after the application of suitable local filtering operations, which in turn are some special stochastic local operations assisted with classical communication (SLOCC). In the present work, we introduce the notion of hidden non n-locality. The notion is detailed using a bilocal network. We provide instances of hidden non bilocality and non trilocality, where we notice quite intriguingly that non bilocality is observed even when one of the sources distributes a mixed two-qubit separable state. Furthermore a characterization of hidden non bilocality is also provided in terms of the Bloch-Fano decomposition, wherein we conjecture that to witness hidden non bilocality, one of the two states (used by the sources) must have non-null Bloch vectors.

Violation of Bell's inequality has been the mainspring for secure key generation in an entanglement assisted Quantum Key Distribution (QKD) protocol. Various contributions have relied on the violation of Bell inequalities to build an appropriate QKD protocol. Residing between Bell nonlocality and entanglement, there exists a hybrid trait of correlations, namely correlations exhibited through the violation of steering inequalities. However, such correlations have not been put to use in QKD protocols as much as their stronger counterpart, the Bell violations. In the present work, we show that the violations of the Cavalcanti–Jones–Wiseman–Reid (CJWR) steering inequalities can act as key ingredients in an entanglement assisted QKD protocol. We work with arbitrary two-qubit entangled states, and characterize them by their utility in such protocols. The characterization is based on the quantum bit error rate and violation of the CJWR inequality. Furthermore, we show that subsequent applications of local filtering operations on initially entangled states exhibiting no violation, lead to violations necessary for the successful implementation of the protocol. An additional vindication of our protocol is provided by the use of absolutely Bell–Clauser–Horne–Shimony–Holt (Bell–CHSH) local states, states which remain Bell–CHSH local even under global unitary operations.Quanta 2023; 12: 1–21.

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