A triple point in 3-level systems
  The energy spectrum of a 3-level atomic system in the $\Xi$-configuration is studied. This configuration presents a triple point independently of the number of atoms, which remains in the thermo- dynamic limit. This means that in a vicinity of this point any quantum fluctuation will drastically change the composition of the ground state of the system. We study the expectation values of the atomic population of each level, the number of photons, and the probability distribution of photons at the triple point. 
E. Nahmad-Achar, S. Cordero, R. L\'opez-Pe\~na, and O. Casta\~nos
quant-ph