Quantum entanglement and pairing correlation in the reduced BCS pairing model

Using the particle-hole version of the density-matrix renormalization-group technique, the pairing correlation and the quantum entanglement of the reduced BCS pairing model are investigated. Both of them behave smoothly from the weak to the strong coupling regimes. A convergence radius (∼1/ln Ω) of condensation energy is detected by the first order derivative of the block-block entanglement. Furthermore, the block-block entanglement in the strong coupling regime shows distinct size dependence, and a logarithmic volume law is suggested numerically.