Characterization of entanglement in multiqubit systems via spin squeezing

TL;DR

This paper investigates how spin squeezing in symmetric multiqubit systems relates to pairwise entanglement, using local invariants and covariance matrix analysis to characterize entanglement properties.

Contribution

It introduces a complete set of local invariants for symmetric two-qubit systems and links collective spin squeezing to pairwise entanglement measures.

Findings

Spin squeezing correlates with pairwise entanglement in symmetric multiqubit states.

Off-diagonal covariance matrix blocks fully capture collective pairwise entanglement.

Local invariants effectively characterize symmetric two-qubit entanglement.

Abstract

Quantum entanglement reflects itself through non-local correlations among the subsystems of a quantum system. This thesis focuses on constructing a complete set of local invariants characterizing symmetric two qubit systems and analyzing the pairwise entanglement properties like collective spin squeezing - exhibited by multiqubits - in terms of two qubit entanglement invariants. Further, the collective pairwise entanglement properties of symmetric multiqubit states are shown to be captured entirely by the off diagonal block of the covariance matrix.