Super-quantum states in SU(2) invariant $3 \times N$ level systems

TL;DR

This paper investigates super-quantum states in SU(2) invariant 3×N level systems, revealing their universal geometric structure and properties related to their rank and classicality under generalized local hidden variables.

Contribution

It provides a geometric characterization of super-quantum states and analyzes their rank properties, extending understanding of nonclassicality in quantum systems.

Findings

Super-quantum states form a line segment in the state manifold.

These states can be highly mixed but have a rank less than states with GLHV description.

All super-quantum states admit a universal geometric description.

Abstract

Nonclassicality of quantum states is expressed in many shades, the most stringent of them being a new standard introduced recently in [Phys. Rev. A 89, 062110 (2014)]. This is accomplished by expanding the notion of local hidden variables (LHV) to generalised local hidden variables (GLHV), which renders many nonlocal states also classical. We investigate these super-quantum states (called exceptional in [Phys. Rev. A 89, 062110 (2014)]) in the family of $SU(2)$ invariant $3 \times N$ level systems. We show that all super-quantum states admit a universal geometrical description, and that they are most likely to lie on a line segment in the manifold, irrespective of the value of $N$. We also show that though the super - quantum states can be highly mixed, its relative rank with respect to the uniform state is always less than that of a state which admits a GLHV description.