Rabi precession

This mixed classical/quantum expression is valid for classical nuclear behavior and, strictly speaking, for the case of direct two-site interaction rather than superexchange, as the Landau-Zener expression was derived from the time-dependent Schrodinger equation assuming a two-state (reactant/product) electronic system with direct coupling. Nevertheless, it becomes clear on physical grounds that the form of Eqs. 4-5 can serve to define an effective A in the superexchange case in terms of the Rabi precession frequency characteristic of the two trap sites embedded in the complex system wherein 2A/h would be computed from this net effective Rabi precession frequency. 

Cohen-Tannoudji, C., Avan, P. Discrete states coupled to a continuum Continuous transition between Rabi precession and the Weisskopf-Wigner exponential decay. In C.N.R.S. Colloquium Etats Atomiques et Moleculaires Couples 4 un Continuum, p. 93. Aussois, France. Paris Editions du CNRS no. 273... 

In principle the photophysical dynamics of a molecule under coherent excitation has two components. In the coherent motion driven by the laser field, the pseudospin representing the density matrix of the electronic system performs a Rabi precession between the singlet ground and excited states. Additionally, incoherent transitions through coupling to the vacuum field modes or to intramolecular vibrational modes will cause radiative and non-radiative population transfer between the electronic... 

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