which form the vertices of a regular tetrahedron in the Bloch sphere. The projectors that define the SIC-POVM are given by Π Π i = | ψ ψ i ⟩ ⟩ ⟨ ⟨ ψ ψ i | , and the elements of the SIC-POVM are thus F i = Π Π i / 2 = | ψ ψ i ⟩ ⟩ ⟨ ⟨ ψ ψ i | / 2 .