We propose a mean-field approach to the Duffing oscillator to construct perturbatively the bounded operators that generate the quantum states, and to define a non-Gaussian density operator.
Cite
@article{arxiv.physics/9702018,
title = {Mean Field Approach to Quantum Duffing Oscillator},
author = {Sang Pyo Kim},
journal= {arXiv preprint arXiv:physics/9702018},
year = {2008}
}