Negativity of the Wigner function as an indicator of nonclassicality
  A measure of nonclassicality of quantum states based on the volume of the negative part of the Wigner function is proposed. We analyze this quantity for Fock states, squeezed displaced Fock states and cat-like states defined as coherent superposition of two Gaussian wave packets. 
Anatole Kenfack and Karol Zyczkowski