Squeezing in the Schrodinger picture: normal ordering technique to solve the mass-varying oscillator

Recent papers by Cheng and Fung (1988) and Lo (1990) have studied the generation of squeezed states out of coherent states in systems described by some time-dependent Hamiltonians. They have employed the evolution operator method for the Schrodinger equation with a Hamiltonian expressible as H(t)=al(t)J++a2(t)J0++a3 (t)J-, where J+-,J0 are the SU(2) group generators. Here, for the sake of comparison of methods and results, the present authors employ the normal ordered Hamiltonian H(t)= Sigma hl,m(t)(a)lam and investigate squeezing through an alternative approach using the normal ordering technique to solve the evolution operator for the same system.