Tripartite continuous-variable entanglement of NOPA system

We investigate the fundamental limits to the achievable tripartite continuous-variable (CV) entanglement criterion of a generalized V₁ criterion. Our numerical simulation results show that the non-degenerate eigenvalues do effect the performances of the estimated minimum variances. From below the threshold to above the threshold, with the increase of the pump parameter, the tripartite CV entanglement gradually disappears. The different off-diagonal elements seriously distort the weights for entanglement. We can obtain a good tripartite CV entanglement by appropriately controlling the values of off-diagonal elements ε_ij.