Hidden quantum nonlocality revealed by local filters

Karin Berndl, Stefan Teufel

Adán Cabello

Tanumoy Pramanik, Young‐Wook Cho, Sang-Wook Han +3 more

Nonlocal quantum correlation is at the heart of the bizarre nature of quantum physics. While there are various classes of nonlocal quantum correlation, steerability of a quantum state by local measurements provides unique operational features. Here, we theoretically and experimentally investigate the ``hidden'' property of quantum steerability. In particular, we find that there are initially unsteerable states which can reveal the steerability by using local filters on individual quantum systems. It is remarkable that a certain set of local filters is more effective in revealing steerability than Bell nonlocality whereas there exists another set of filters that is more effective in revealing Bell nonlocality than steerability. This result suggests the structural difference between entanglement and steerability. Finally, we present a counterintuitive result that mixed states originating from nonmaximally pure entangled states can have hidden steerability while the mixed state from a maximally pure entangled state fails to show steerability.

Lingyun Sun, Li Xu, Jing Wang +4 more

Nonlocal quantum correlations among the quantum subsystems play essential roles in quantum science. The violation of the Svetlichny inequality provides sufficient conditions of genuine tripartite nonlocality. We provide tight upper bounds on the maximal quantum value of the Svetlichny operators under local filtering operations, and present a qualitative analytical analysis on the hidden genuine nonlocality for three-qubit systems. We investigate in detail two classes of three-qubit states whose hidden genuine nonlocalities can be revealed by local filtering.

Daniel Cavalcanti, Mafalda L. Almeida, Valerio Scarani +1 more

S. Camalet

We show that any Bell local state with a hidden nonlocality that can be revealed by local filtering is more, or equally, entangled than nonlocal states. More precisely, it can be deterministically transformed into a nonlocal state by local operations and classical communication. For such a state, there is a clear anomaly of nonlocality for any measures of entanglement and nonlocality. Moreover, we prove that the hidden nonlocality of any bipartite state more, or equally, entangled than nonlocal states can be revealed by local operations and the sending of two one-bit messages, one in each direction. For some particular states, one bit of communication is even enough.