Spin squeezing criterion with local unitary invariance

Abstract

We propose a new spin squeezing criterion for arbitrary multi-qubit states that is invariant under local unitary operations. We find that, for arbitrary pure two-qubit states, spin squeezing is equivalent to entanglement, and multi-qubit states are entangled if this new spin squeezing parameter is less than 1.

6 pages. Version 3: Small corrections

References in corpus (1)

• Characterizing the entanglement of symmetric many-particle spin-1/2 systems

Cited by in corpus (2)

• Local Invariants and Pairwise Entanglement in Symmetric Multi-qubit System
• Equivalence between two-mode spin squeezed states and pure entangled states with equal spin