Multicriticality and quantum fluctuation in a generalized Dicke model

Quantum many-body systems that support high-order quantum phase transitions are quite rare. Here we consider an important generalization of the Dicke model in which an ensemble of multilevel atoms, instead of two-level atoms as in the conventional Dicke model, interact with a single photonic mode, and show that this generalized Dicke model can become multicritical. For a subclass of experimentally realizable schemes, multicritical conditions of arbitrary order can be expressed analytically in compact forms. As such, experiments can be readily designed to achieve quantum phase transition of desired order. We also calculate the atom-photon entanglement entropy for both critical and noncritical cases and find that the order of the criticality strongly affects the critical entanglement entropy: higher order yields stronger entanglement. Our work provides deep insight into quantum phase transitions and multicriticality.

Automated summary

This study explores a significant generalization of the Dicke model, where a set of multilevel atoms interact with a photon mode, leading to the possibility of achieving multicritical conditions and designing experiments to achieve quantum phase transitions of desired order. The research also reveals that the order of criticality strongly influences the critical entanglement entropy, with higher order resulting in stronger entanglement. This work provides valuable insights into quantum phase transitions and multicriticality.