  The old problem exists for a driven (time-dependent) quantum oscillator: to
differ the true vacuum state from the squeezed one. We suggest finding the true
vacuum state by minimization of the functional containing the difference of the
potential and kinetic energies of oscillator. Analytical and numerical examples
confirming this offer are considered.

Quantum Physics;General Relativity and Quantum Cosmology;High Energy Physics - Theory;Computational Physics