2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/89357The set of all separable quantum states is compact and convex. We focus on the two-qubit quanum system and study the boundary of the set. Then we give the criterion to determine whether a separable state is on the boundary. Some straightforward geometrical interpretations for entanglement are based on the concept and presented subsequently.Quantum Physicstext