Theorem on nonclassical states

Let the density matrix of an arbitrary state be expressed in terms of number states as {ρ}^=∑ₙ₌₀^∞{{∑}}ₘ₌₀^{{{∞}}}${ρ}(n,m){}n〉〈m mU. We prove the following theorem: If {ρ}(0,0)=0, then the state is as nonclassical as possible according to the measure introduced by Lee [Phys. Rev. A 44, R2775 (1991)].