Exploring chaos in Dicke Model using ground state fidelity and Loschmidt   echo
  We study the quantum critical behaviour of the Dicke Hamiltonian, with finite number of atoms and explore the signature of quantum chaos using measures like the ground state fidelity and the Loschmidt echo. We show that both these quantities clearly point to the chaotic nature of the system in the super-radiant phase. 
Utso Bhattacharya, Sayak Dasgupta and Amit Dutta
cond-mat.stat-mech quant-ph