Fig. 1
From: A geometric formulation to measure global and genuine entanglement in three-qubit systems
Entanglement–polytope \(\mathcal {P} \subset \mathbb {R}^3\) associated with the three-qubit states (1). It is a body that resembles two tetrahedra, joined at their base, embedded in a cube with edges of length equal to 1/2. The parameter \(\lambda _k\) (defining the corresponding axis) is the smallest eigenvalue of the density matrix associated with the kth qubit. Vertex \(\vec {S}\) represents the entire set of fully separable states while \(\vec {G}\) corresponds to the Greenberger–Horne–Zeilinger state. The vertices \(\vec {B}_i\) correspond to bi-separable states \(\vert \phi _i \rangle \vert \phi _{jk} \rangle\), with \(\vert \phi _i \rangle\) the state of the ith qubit and \(\vert \phi _{jk} \rangle\) a Bell state in the bipartition \(i-jk\).
