Bell-type inequalities à la Schrödinger

Yan Gu, Haifeng Zhang, Zhigang Song +2 more

In terms of quantum probability statistics, the Bell inequality (BI) and its violation are extended to spin-[Formula: see text] entangled Schrödinger cat state (called the Bell cat state) with both parallel and antiparallel spin-polarizations. Except the spin-1/2, the BI is never ever violated by the Bell cat states with the measuring outcomes including entire Hilbert space. If, on the other hand, measuring outcomes are restricted in the subspace of spin coherent state (SCS), a universal Bell-type inequality (UBI), [Formula: see text], is formulated in terms of the local realistic model. We observe a spin parity effect that the UBI can be violated only by the Bell cat states of half-integer but not the integer spins. The violation of UBI is seen to be a direct result of nontrivial Berry phase between the SCSs of south- and north-pole gauges for half-integer spin, while the geometric phase is trivial for the integer spins. A maximum violation bound of UBI is found as [Formula: see text], which is valid for arbitrary half-integer spin-[Formula: see text] states.

H. E. Andås

Yu-Chun Wu, Marek Żukowski

A technique, which we call homogenization, is applied to transform Clauser and Horne- (CH)-type Bell inequalities that contain lower-order correlations into CH, Shimony, and Holt- (CHSH)-type Bell inequalities, which are defined for highest-order correlation functions. A homogenization leads to inequalities involving more settings, that is, a choice of one more observable is possible for each party. We show that this technique preserves the tightness of Bell inequalities: A homogenization of a tight CH-type Bell inequality is still a tight CHSH-type Bell inequality. As an example, we obtain $3\ifmmode\times\else\texttimes\fi{}3\ifmmode\times\else\texttimes\fi{}3$ CHSH-type Bell inequalities by the homogenization of $2\ifmmode\times\else\texttimes\fi{}2\ifmmode\times\else\texttimes\fi{}2$ CH-type Bell inequalities derived by Sliwa [Phys. Lett. A 317, 165 (2003)].

Boris S. Tsirelson

Li‐Yi Hsu

We investigate the Bell-type inequalities of graph states. In this paper, Bell-type inequalities can be derived based on two kinds of the associated subgraphs of the graph states. First, the star subgraphs lead to the maximal violation of the modified Seevinck-Svetlichny inequalities. Second, cycle subgraphs lead to maximal violation of Bell-type inequalities. As a result, once the associated graph of a graph state is given, the corresponding Bell operators can be immediatedly determined using stabilizing generators. In the above Bell-type inequalities, two measurement settings for each party are required.

Enrico G. Beltrametti, Maciej Mączyński