Higher order wave-particle duality
  The complementarity of single-photon's particle-like and wave-like behaviors can be described by the inequality $D^2+V^2 \leq 1$, with $D$ being the path distinguishability and $V$ being the fringe visibility. In this paper, we generalize this duality relation to multi-photon case, where two new concepts, higher order distinguishability and higher order fringe visibility, are introduced to quantify the higher order particle-like and wave-like behaviors of multi-photons. 
Jie-Hui Huang, Sabine W\"olk, Shi-Yao Zhu, and M. Suhail Zubairy
quant-ph