Quantum pions

Abstract

We show that two- and three-pion states produced in the decay of neutral kaons are contextual, entangled, and Bell nonlocal in isospin space. By reinterpreting the experimental values of the different isospin amplitudes, we can determine the amount of entanglement enjoyed by these states and the extent to which they violate the non-contextuality and Bell locality inequalities. Notably, the three-pion state offers a genuine multipartite test of Bell nonlocality with qutrits.

Figures (2)

• Figure 1: Variation of the coefficient $\Gamma$ of the three-pion state across the kinematic space of the two variables $x$ and $y$ of the Dalitz plot, which uses the central values Bijnens:2002vr of the coefficients in Eqs. (\ref{['000']})--(\ref{['0+-']}) and refers to the final state containing charged pions---which is the most restrictive. The area inside the closed curve shows the allowed values for the variables $x$ and $y$.
• Figure 2: Variation of the value of ${\cal I}_3'$ across the kinematic space of the two variables $x$ and $y$ of the same Dalitz plot as in Fig. \ref{['fig:gamma']}. The area inside the closed curve shows the allowed values for the variables $x$ and $y$. The critical value ${\cal I}_3'=4$ is marked by the white dashed contour.