Consider a chain of N qubits, described by the function | Ψ Ψ ⟩ ⟩ ∈ ∈ H ⊗ ⊗ N . The most natural way of describing | Ψ Ψ ⟩ ⟩ would be using the local M N -dimensional basis | i 1 , i 2 , . . , i N − − 1 , i N ⟩ ⟩ : | Ψ Ψ ⟩ ⟩ = ∑ ∑ i = 1 M c i 1 i 2 . . i N | i 1 , i 2 , . . , i N − − 1 , i N ⟩ ⟩ where M is the on-site dimension.