Localization measures of parity adapted U(D)-spin coherent states applied to the phase space analysis of the D-level Lipkin-Meshkov-Glick model

We study phase space properties of critical, parity symmetric, N-qudit systems undergoing a quantum phase transition (QPT) in the thermodynamic N & INFIN; limit. The D = 3 level (qutrit) Lipkin-Meshkov-Glick model is eventually examined as a particular example. For this purpose, we consider U(D )-spin coherent states (DSCS), generalizing the standard D = 2 atomic coherent states, to define the coherent state representation Q & psi; (Husimi function) of a symmetric N-qudit state |& psi;) in the phase space CPD-1 (complex projective manifold). DSCS are good variational approximations to the ground state of an N-qudit system, especially in the N & INFIN; limit, where the discrete parity symmetry ZD-1 2 is spontaneously broken. For finite N, parity can be restored by projecting DSCS onto 2D-1 different parity invariant subspaces, which define generalized Schrodinger cat states reproducing quite faithfully low-lying Hamiltonian eigenstates obtained by numerical diagonalization. Precursors of the QPT are then visualized for finite N by plotting the Husimi function of these parity projected DSCS in phase space, together with their Husimi moments and Wehrl entropy, in the neighborhood of the critical points. These are good localization measures and markers of the QPT.

Automated summary

We study the phase space properties of critical, parity symmetric, N-qudit systems undergoing quantum phase transitions (QPTs) in the thermodynamic N → ∞ limit. We specifically examine the D = 3 level Lipkin-Meshkov-Glick model as an example. By considering U(D)-spin coherent states (DSCS) as a representation of symmetric N-qudit states in the phase space CPD-1, we can visualize precursors of QPTs for finite N through the Husimi function, Husimi moments, and Wehrl entropy.