Entanglement Dynamics of Photon-Added Quasi-Bell Coherent States

Photon-added coherent states (PACS) represent a critical bridge between classical coherent states and quantum Fock states, exhibiting non-classical properties such as squeezing and sub-Poissonian statistics. In this work, we investigate the entanglement properties of quasi-Bell states constructed from photon-added coherent states, with a focus on the concurrence and entanglement of formation under varying photon excitation numbers m and coherent state amplitudes |α|. By leveraging the mathematical framework of Glauber’s coherent states and Laguerre polynomial normalization, we derive analytical expressions for the overlap between |α, m⟩ and | − α, m⟩, and analyze their suitability for qubit encoding. Our results reveal that for |α| ≥ 2, these states approximate orthogonal logical qubits, while smaller amplitudes exhibit m-dependent entanglement degradation. Numerical simulations demonstrate that entanglement of formation E12 approaches unity for large |α|, independent of m, but diminishes with increasing m in the weak-field regime (|α| ² < 1.5). These findings advance the understanding of photon-added states in quantum information protocols, offering insights into decoherence mitigation and resource-efficient qubit design.