Entanglement and Bell-State Preparation in the Tripartite Quantum Rabi Model

How can a simple light-matter interaction reorganize two-qubit entanglement, and can that structure be used to prepare a useful quantum state? Our recent preprint studies these questions in the tripartite quantum Rabi model, where two qubits interact collectively with a single bosonic mode.

In the zero-detuning limit, the spectrum separates into branches with sharply different entanglement properties. Some triplet states carry no two-qubit entanglement, while others are maximally entangled; the antisymmetric singlet ladder remains decoupled. Finite detuning turns selected crossings into avoided crossings, allowing entanglement to move between eigenbranches.

This spectral picture suggests a state-preparation strategy. Starting from a nearly separable state at weak coupling, one can slowly increase the collective coupling and follow an eigenbranch that becomes dominated by a Bell-state component. A compact three-state model explains the relevant mixing, while finite-time simulations identify the coupling strength and ramp duration needed for high final fidelity.

The work links a static question, the organization of entanglement in the spectrum, to a dynamical one, the preparation of a Bell state within a finite time.

Read the preprint on arXiv