Some remarks on the coherent-state variational approach to nonlinear boson models

Abstract

The mean-field pictures based on the standard time-dependent variational approach have widely been used in the study of nonlinear many-boson systems such as the Bose-Hubbard model. The mean-field schemes relevant to Gutzwiller-like trial states $|F>$, number-preserving states $|\xi >$ and Glauber-like trial states $|Z>$ are compared to evidence the specific properties of such schemes. After deriving the Hamiltonian picture relevant to $|Z>$ from that based on $|F>$, the latter is shown to exhibit a Poisson algebra equipped with a Weyl-Heisenberg subalgebra which preludes to the $|Z>$-based picture. Then states $|Z>$ are shown to be a superposition of $\mathcal{N}$-boson states $|\xi >$ and the similarities/differences of the $|Z>$-based and $|\xi >$-based pictures are discussed. Finally, after proving that the simple, symmetric state $|\xi >$ indeed corresponds to a SU(M) coherent state, a dual version of states $|Z>$ and $|\xi >$ in terms of momentum-mode operators is discussed together with some applications.

16 pages

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