Quantumness Beyond Entanglement: The Case of Symmetric States

TL;DR

This paper explores quantum correlations beyond entanglement in symmetric states, proposing a measure based on modal decompositions and analyzing extremal states with minimal and maximal quantumness.

Contribution

It introduces a novel measure of quantumness for symmetric states that captures quantum correlations beyond entanglement and examines extremal states under this measure.

Findings

SU(2)-coherent states have minimal quantumness

States with maximally spread Majorana constellations have maximal quantumness

Quantum correlations can exist without entanglement in symmetric states

Abstract

It is nowadays accepted that truly quantum correlations can exist even in the absence of entanglement. For the case of symmetric states, a physically trivial unitary transformation can alter a quantum state from entangled to separable and vice versa. We propose to certify the presence of quantumness via an average over all physically relevant modal decompositions. We investigate extremal states for such a measure: SU(2)-coherent states possess the least quantumness whereas the opposite extreme is inhabited by states with maximally spread Majorana constellations.