We explore the theoretical possibility of extending the usual squeezed state to those produced by nonlinear single-mode squeezing operators. We derive the wave functions of exp[−(i g /2)( P + P )|0⟩ in the coordinate representation. A new operator's disentangling formula is derived as a by-product.
We find that the exponential operators U=exp[-i(${\ensuremath{\lambda}}_{1}$Q1P2+${\ensuremath{\lambda}}^{2}$Q2P1] and W=exp[-i(${\ensuremath{\lambda}}_{1}$Q1Q2-${\ensuremath{\lambda}}_{2}$pP1P2)] (where ${\ensuremath{\lambda}}_{1}$ and ${\ensuremath{\lambda}}_{2}$ are real; Pi and Qi are coordinate and momentum operators, respectively; and i=1,2) are two types of generalized squeezing operators responsible for generating two types of one- and two-mode combination squeezed states, respectively. The coordinate and/or momentum representations of U and W are presented, and their normal product forms are first derived in terms of the newly developed technique of integration within an ordered product, which provides us with a direct approach to constructing these new squeezed states. The fluctuations in quadrature phases for these states are analyzed.
We obtain the wave function in the coordinate representation of the one-mode squeezed states \ensuremath{\Vert}\ensuremath{\zeta}, \ensuremath{\alpha}〉=exp(\ensuremath{\zeta}${\mathit{a}}^{\mathrm{^}2}$-${\mathrm{\ensuremath{\zeta}}}^{\mathrm{*}}$a2)exp(\ensuremath{\alpha}${\mathit{a}}^{\mathrm{^}}$-${\mathrm{\ensuremath{\alpha}}}^{\mathrm{*}}$a)\ensuremath{\Vert}0〉. The wave function is a displaced Gaussian with center and width depending upon the parameters \ensuremath{\alpha} and \ensuremath{\zeta}.
We find that the exponential operator V ≡exp[ i λ( Q 1 P 2 + Q 2 P 3 +⋅⋅⋅+ Q n −1 P n + Q n P 1 )], Q i , P i are, respectively, the coordinate and momentum operators, is an n -mode squeezing operator which engenders standard squeezing. By virtue of the technique of integration within an ordered product of operators we derive V 's normally ordered expansion and obtain the n -mode squeezed vacuum states, its Wigner function is calculated by using the Weyl ordering invariance under similar transformations.