there is a minimum in $\xi_{\textsc{svne}}$ at $\lambda = 0$, there is a maximum in this quantity at $\omega_{1} = 0$ ((b)).

![$\xi_{\textsc{svne}}$ vs. $\lambda$ for $N=4, \,k=0,1,2$, for the BEC model. The curves correspond to $k=0$ (red solid), $1$ (blue dashed) and $2$ (green dotted). $\omega_{1}=0.25$. []{data-label="fig:energySpectrumSVNEvaryLambda"}](fig_entropy_4_vary_lambda_omega1_quarter.eps){width="45.00000%"}

We have also calculated the PCC between various indicators and $\xi_{\textsc{svne}}$ for the set of states $\ket{\psi_{4,k}}, \,0\leqslant k \leqslant 4$, using $100$ values of each of the $\xi$-indicators calculated for each $\lambda$ in the range $[-1, 1]$ with a step size of $0.02$. The results are very similar to those already found (see figure \[fig:CorrPlotN4VaryOmega1\]) using $\omega_{1}$ as the variable parameter instead of $\lambda$.

Atom-field interaction model
----------------------------

We turn next to the case of a multi-level atom (modelled by an anharmonic oscillator) that is linearly coupled with strength $g$ to a radiation field of frequency $\omega_{\mathrm{f}}$. The effective Hamiltonian (setting $\hbar = 1$ ) is given by [@agarwalpuri] $$H_{\textsc{af}}=\omega_{\mathrm{f}} a^{\dagger} a +
 \omega_{\mathrm{a}} b^{\dagger} b + \gamma b^{\dagger \,2} b^{2} + g ( a^{\dagger} b + a b^{\dagger}).
\label{eqn:HAF}$$ $\omega_{\mathrm{a}}$ and $\gamma$ ($> 0$ for stability) are constants. $(a,a^{\dagger})$ and $(b,b^{\dagger})$ are the annihilation and creation operators for the field 