The exact convex roof for GHZ-W mixtures for three qubits and beyond
This paper presents an exact solution for the convex roof of the square root of the three-tangle for rank-two density matrices and all states within the Bloch sphere, identifying new optimal tetrahedra and triangular decompositions governed by a "zero-state locking" property that extends to all SL-invariant GHZ and W states and is applicable to arbitrary qubit numbers.