Emergent Universality in a Quantum Tricritical Dicke Model

Area of Science:

• Quantum physics
• Condensed matter theory
• Statistical mechanics

Background:

• The Dicke model describes light-matter interactions.
• Quantum phase transitions occur at zero temperature.
• Tricritical points represent a confluence of first- and second-order phase transitions.

Purpose of the Study:

• To propose and analyze a generalized Dicke model exhibiting a quantum tricritical point.
• To map the phase diagram and investigate critical behavior.
• To explore universality at the tricritical point.

Main Methods:

• Exact solution using a low-energy effective Hamiltonian.
• Analysis in the thermodynamic limit.
• Application of Landau theory of phase transitions.

Main Results:

• The model supports a quantum tricritical point.
• The order parameter exhibits nonuniversality at the tricritical point, consistent with Landau theory.
• A universal relation between excitation gap and entanglement entropy is found along the critical line.

Conclusions:

• The separation of classical and quantum degrees of freedom is key to the observed universality.
• Universality is governed by emergent quantum modes, while the order parameter is classically determined.
• This work provides insights into critical phenomena in quantum many-body systems.