Bipartite qutrit local realist inequalities and the robustness of their quantum mechanical violation

TL;DR

This paper introduces new bipartite qutrit local realist inequalities based on Wigner's argument, compares their quantum violations with CGLMP inequalities, and finds that their robustness varies with measurement type and state.

Contribution

The paper formulates generalized Wigner inequalities for bipartite qutrits that are distinct from CGLMP inequalities and analyzes their quantum violation robustness.

Findings

GWI are violated by quantum mechanics for bipartite qutrit states.

QM violation of GWI is more robust than CGLMP for certain observables and states.

Robustness of quantum violation depends on measurement type and state.

Abstract

Distinct from the type of local realist inequality (known as the Collins-Gisin-Linden-Massar-Popescu or CGLMP inequality) usually used for bipartite qutrit systems, we formulate a new set of local realist inequalities for bipartite qutrits by generalizing Wigner's argument that was originally formulated for the bipartite qubit singlet state. This treatment assumes existence of the overall joint probability distributions in the underlying stochastic hidden variable space for the measurement outcomes pertaining to the relevant trichotomic observables, satisfying the locality condition and yielding the measurable marginal probabilities. Such generalized Wigner inequalities (GWI) do not reduce to Bell-CHSH type inequalities by clubbing any two outcomes, and are violated by quantum mechanics (QM) for both the bipartite qutrit isotropic and singlet states using trichotomic observables defined by six-port beam splitter as well as by the spin-$1$ component observables. The efficacy of GWI is then probed in these cases by comparing the QM violation of GWI with that obtained for the CGLMP inequality. This comparison is done by incorporating white noise in the singlet and isotropic qutrit states. It is found that for the six-port beam splitter observables, QM violation of GWI is more robust than that of the CGLMP inequality for singlet qutrit states, while for isotropic qutrit states, QM violation of the CGLMP inequality is more robust. On the other hand, for the spin-$1$ component observables, QM violation of GWI is more robust for both the type of states considered.