Position states | q ⟩ ⟩ and momentum states | p ⟩ ⟩ are eigenvectors of Hermitian operators x ^ ^ and − − i ∂ ∂ ∂ ∂ x , respectively. Weigert and Wilkinson were first to notice that also a linear combination of these operators have eigenbases, which have some features typical for the mutually unbiased bases. An operator α α x ^ ^ − − i β β ∂ ∂ ∂ ∂ x has eigenfunctions proportional to exp ⁡ ⁡ ( i ( a x 2 + b x ) ) with α α + 2 β β a = 0 and the corresponding eigenvalues b β β . If we parametrize α α and β β as cos ⁡ ⁡ θ θ and sin ⁡ ⁡ θ θ , the overlap between any eigenstate of the linear combination and any eigenstate of the position operator (both states normalized to the Dirac delta) is constant, but dependent on β β :