  Effects of time-dependent applied fields on quantum coupled double-well (DW)
systems with Razavy's hyperbolic potential have been studied. By solving the
Schr\"{o}dinger equation for the DW system, we have obtained time-dependent
occupation probabilities of the eigenstates, from which expectation values of
positions $x_1$ and $x_2$ of particles ($<x_1+x_2 >$), the correlation
($\Gamma(t)$) and the concurrence ($C(t)$) expressing a degree of the
entanglement of the coupled DW system, are obtained. Analytical expressions for
$<x_1+x_2 >$, $\Gamma(t)$ and $C(t)$ are derived with the use of the
rotating-wave approximation (RWA) for sinusoidal fields. Model calculations
have indicated that $<x_1+x_2 >$, $\Gamma(t)$ and $C(t)$ show very complicated
time dependences. Results of the RWA are in good agreement with exact ones
evaluated by numerical methods for cases of weak couplings and small applied
fields in the near-resonant condition. Applications of our method to step
fields are also studied.
