2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/91005We 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 correctionsQuantum Physicstext