DYNAMICAL LOCALIZATION-DELOCALIZATION TRANSITION IN 2-LEVEL NONLINEAR-SYSTEMS DRIVEN BY LASER FIELD

We study the dynamical behavior of an electron in a two-level nonlinea r system driven by a laser field. Two different kinds of systems are s tudied here: (i) Both levels (or sites) have equal nonlinearity streng th (chi), and (ii) the initial excitation site has the nonlinearity st rength but the other site does not have any nonlinearity. In the first case we find that perfect delocalization occurs when the field freque ncy is equal to the energy difference (epsilon(0)) between the two lev els irrespective of the nonlinearity strength but for a particular fix ed critical value of laser field amplitude given by V-c similar to 0.4 714 chi. In the second case we find that the resonance frequency (omeg a(0)) depends on the strength of nonlinearity and the dependence is gi ven by omega(0) = 0.5 chi + epsilon(0) In this case we find that a cri tical field strength given by V-c similar to 0.2456 chi is necessary t o obtain resonance.