We discuss the unitary operator corresponding to the general two-mode coordinate-momentum mixed transformation , where and are arbitrary real numbers. Suitably selecting the parameters and , we obtain a new two-mode bosonic realization of the Lie algebra. We also study the squeezing effects of the squeezed vacuum associated with the new two-mode bosonic realization of the Lie algebra. The results show that the new squeezed vacuum does not possess second-order squeezing, but exhibits higher-order squeezing.
By the complex multimode Bogoliubov transformation, we obtain the general forms of squeeze operators and squeezed states including squeezed vacuum states, squeezed coherent states, squeezed Fock states and squeezed coherent Fock states, for a general multimode boson system. We decompose the squeezed operator into disentangling form in normal ordering to simplify the expressions of the squeezed states. We also calculate the statistical properties of the SS. Furthermore we prove that if it is non-degenerate, a Bogoliubov transformation matrix can be decomposed into three basic matrix, by which we can not only check the criterion of the minimum uncertainty state (MUS) found by Milburn, but also prove that except the special cases, any multimode squeezed state is MUS after the original creation and annihilation operators rotate properly. We also discuss some special cases of the three basic matrices. Finally we give an analytical results of a two-mode system as an example.
Squeezed state is theoretically obtained by performing the squeezing operator on an initial state.Due to non-commutable operators each other,it is not easy to directly obtain the explicit expression of squeezed state.Here,a general approach is provided for deriving the squeezed state′s explicit form,namely,by virtue of the Weyl-Wigner correspondence scheme the explicit forms of single-mode and two-mode squeezed state is obtained,respectively.Without disentangling the squeezing operator,this adopted method is applicable to explicitly solve the general multimode case.
We propose a displacement-operator approach to some aspects of squeezed states for general multiphoton systems. The explicit displacement-operators of the squeezed vacuum and the coherent states are achieved and expresses as the ordinary exponential form. As a byproduct the coherent states of the q-oscillator are obtained by the {\it usual exponential} displacement-operator.