Figure 1
From: Spatio-Temporal Steering for Testing Nonclassical Correlations in Quantum Networks
(a) Schematic diagram of spatio-temporal steering. At time t = 0, a system A (which may be entangled with a system B) is subject to a local measurement with one of the measurement settings {x}, which is described by a positive-operator-valued measure {F a|x } a . After this measurement, the post-measurement composite state ρ a|x is sent into a quantum channel Λ and evolves for a time period t. After many rounds of the experiment, the set of subnormalized quantum states of the system B is denoted as \({\{{\sigma }_{a|x}^{{\rm{ST}}}(t)\}}_{a,x}\). With some appropriate ρ 0, {F a|x } a,x , and Λ, the assemblage \({\{{\sigma }_{a|x}^{{\rm{ST}}}(t)\}}_{a,x}\) does not admit the spatio-temporal hidden-state model equation (3). We call this spatio-temporal steering and refer the assemblage \({\{{\sigma }_{a|x}^{{\rm{ST}}}(t)\}}_{a,x}\) as spatio-temporal steerable. (b) A schematic example of a quantum network with damage (strong dissipation or dephasing, or an entirely broken link). The STS weight and robustness can be employed as diagnostic tools to check whether site-A and site-B are nonclassically correlated.
