Bipartite and tripartite entanglement in the two-qubit quantum Rabi model

This study investigates the entanglement dynamics of the two-qubit quantum Rabi model (QRM) with both homogeneous and inhomogeneous couplings using the adiabatic approximation. The quantized field is initially prepared in a coherent state, while a separable state and a maximally entangled Bell state are selected as the initial two-qubit states. We characterize distinct types of entanglement generated among the subsystems through qubit-field interactions, with a focus on the bipartite entanglement between a single qubit and the field. Building on this, we examine tripartite correlations through the I-residual tangle, a measure that conclusively verifies the presence of genuine tripartite entanglement among the two qubits and the field. This work provides insights into the generation of tunable multipartite entanglement and the detection of quantum phase transitions in light-matter systems, such as circuit quantum electrodynamics (QED).