  We propose a generalized Dicke model which supports a quantum tricritical
point. We map out the phase diagram and investigate the critical behaviors of
the model through exact low-energy effective Hamiltonian in the thermodynamic
limit. As predicted by the Landau theory of phase transition, the order
parameter shows non-universality at the tricritical point. Nevertheless, as a
result of the separation of the classical and the quantum degrees of freedom,
we find a universal relation between the excitation gap and the entanglement
entropy for the entire critical line including the tricritical point. Here the
universality is carried by the emergent quantum modes, whereas the order
parameter is determined classically.
