DISSIPATIVE TUNNELING WITH PERIODIC POLYCHROMATIC DRIVING - EXACT RESULTS AND TRACTABLE APPROXIMATIONS

We investigate the long-time dynamics in dissipative two-level-systems (TLS) when driven by - monochromatic or pulse-shaped - periodic field s. The environmental influence is investigated within the noninteracti ng-blip appoximation (NIBA), while no restrictions are assumed on the driving force. With the focus being on electron-transfer (ET) reaction s in condensed media, we consider a continuous Ohmic spectrum for the bath modes. The asymptotic dynamics exhibits always the periodicity of the external force. The induced oscillations show a smooth periodic b ehavior which becomes richer, if, for example, multiphoton resonances occur. For monochromatic driving, the oscillatory multiresonance patte rn becomes gradually smoothed out when the temperature, and/or the Ohm ic strength are sufficiently high. It may persist, however, for pulse- shaped driving. Exact NIBA analytical and/or numerical solutions, for both the Ohmic transfer rate and for the driven dynamics, are used to determine the validity range of the short-time approximation for the b ath correlation functions. The latter is frequently employed to invest igate the ET dynamics. Our analysis shows that the short-time approxim ation may give qualitative incorrect results at low temperatures. (C) 1997 Elsevier Science B.V.