Dynamical localization-delocalization transition in two-level nonlinear systems driven by laser field

Abstract

We study the dynamical behavior of an electron in a two-level nonlinear system driven by a laser field. Two different kinds of systems are studied here: (i) Both levels (or sites) have equal nonlinearity strength (χ), and (ii) the initial excitation site has the nonlinearity strength but the other site does not have any nonlinearity. In the first case we find that perfect delocalization occurs when the field frequency is equal to the energy difference (ε₀) between the two levels irrespective of the nonlinearity strength but for a particular fixed critical value of laser field amplitude given by V_c≈0.4714χ. In the second case we find that the resonance frequency (ω₀) depends on the strength of nonlinearity and the dependence is given by ω₀=0.5χ + ε₀. In this case we find that a critical field strength given by V_c≈0.2456χ is necessary to obtain resonance.