Figure 3

Nonlinearity of the undriven Duffing potential. Top: the nonlinearity measures \(\eta_{{ \mathrm{B}} } [{V} ]\) (red line) and \(\eta_{ { \mathrm{N G}} } [{V} ]\) (blue line) for the undriven oscillator as a function of ε. The inset is a parametric plot of \(\eta_{{ \mathrm{B}} }\) as a function of \(\eta_{ { \mathrm{N G}} }\), showing that the two measures are monotone functions of each other. The bottom panel shows the Wigner function of the GS for \(\varepsilon=0.1\).