2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/91304By using of a special reduction way of density matrices, in this Letter we find the entanglement between two bunches of particles, its measure can be represented by the entanglement of formation.REVTeX, 5 pages, no figureQuantum PhysicsSpecial reduction of density matrixes and entanglement between two bunches of particlestext