Local Realism of Macroscopic Correlations

We identify conditions under which correlations resulting from quantum measurements performed on macroscopic systems (systems composed of a number of particles of the order of the Avogadro number) can be described by local realism. We argue that the emergence of local realism at the macroscopic level is caused by an interplay between the monogamous nature of quantum correlations and the fact that macroscopic measurements do not reveal properties of individual particles.

Figure 1

The three stages of the LHV strategy outlined in the text. (i) A system with four regions ($X=A$, $B$, $C$, $D$) of $N_X$ particles (shown as circles), measured with $S_X$ different settings. As explained in the text, an effective state ${\rho }_{\mathrm{eff}}$ for these measurements can be found and is shown in (ii) where the squares depict effective particles. (iii) denotes the symmetric extension of ${\rho }_{\mathrm{eff}}$ to a state ${\sigma }_N$ of $S_X$ particles (depicted by circles surrounding squares) in each region. In (iii), all the $S_X$ measurements in each region $X$ commute, implying the existence of the joint probability distribution and therefore, an LHV model for the state in (i).