by $$\label{eqn:spintomogram}
w({\mathbf{n}},m)=\bra{{\mathbf{n}},m}\rho_{\textsc{s}}\ket{{\mathbf{n}},m}$$ where $\rho_{\textsc{s}}$ is the qubit density matrix. Corresponding to each value of ${\mathbf{n}}$ there exists a complete basis set. The atomic tomograms are obtained from these, and the corresponding entanglement properties are quantified using appropriate adaptations of the indicators described above. The extension of the foregoing to the multipartite case is straightforward  [@ibort], and the tomograms obtained can be examined on similar lines.

\[sec:work\]Avoided energy-level crossings in bipartite CV models
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The double-well BEC model
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The effective Hamiltonian for the system and its diagonalisation are as follows [@sanz]. Setting $\hbar = 1$, $$H_{\textsc{bec}} =\omega_{0} N_{\mathrm{tot}} + \omega_{1} (a^{\dagger} a - b^{\dagger} b) + U  N_{\mathrm{tot}}^{2} - \lambda (a^{\dagger} b + a b^{\dagger}).
\label{eqn:HBEC}$$ Here, $(a,a^{\dagger})$ and $(b,b^{\dagger})$ are the respective boson annihilation and creation operators of the atoms in wells A and B (the two subsystems), and $N_{\mathrm{tot}} 
= (a^{\dagger} a + b^{\dagger} b)$. $U$ is the strength of nonlinear interactions between atoms within each well, and also between the two wells. $U>0$, ensuring that the energy spectrum is bounded from below. $\lambda$ is the linear interaction strength, while $\omega_{1}$ is the strength of the population imbalance between the two wells. The Hamiltonian is diagonalised by 