The observation of long-lived electronic quantum coherence in a photosynthetic light harvesting system [Engel et al. Nature 2007, 446, 782] has led to much effort being devoted to elucidation of the quantum mechanisms of the photosynthetic excitation energy transfer. In this paper we examine the question of whether the decay of the coherent beating signal is due to quantum mechanical decoherenc...

We provide a very general result that identifies the essential spectrum of broad classes of operators as exactly equal to the closure of the union of the spectra of suitable limits at infinity. Included is a new result on the essential spectra when potentials are asymptotic to isospectral tori. We also recover with a unified framework the HVZ theorem and Krein’s results on orthogonal polynomial...

We provide a very general result that identifies the essential spectrum of broad classes of operators as exactly equal to the closure of the union of the spectra of suitable limits at infinity. Included is a new result on the essential spectra when potentials are asymptotic to isospectral tori. We also recover with a unified framework the HVZ theorem and Krein’s results on orthogonal polynomial...