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F\"orster's theory of resonant energy transfer (FRET) predicts the strength and range of exciton transport between separated molecules. We introduce an exactly soluble model for FRET which reproduces F\"orster's results as well as incorporating quantum coherence effects. As an application the model is used to analyze a system composed of quantum dots and the protein bacteriorhodopsin., Comment: 10 pages, 2 figures

We study the regularized average Renyi output entropy $\bar{S}_{r}^{\reg}$ of quantum channels. This quantity gives information about the average noisiness of the channel output arising from a typical, highly entangled input state in the limit of infinite dimensions. We find a closed expression for $\beta_{r}^{\reg}$, a quantity which we conjecture to be equal to $\Srreg$. We find an explicit form for $\beta_{r}^{\reg}$ for some entanglement-breaking channels, and also for the qubit depolarizing channel $\Delta_{\lambda}$ as a function of the parameter $\lambda$. We prove equality of the two quantities in some cases, in particular we conclude that for $\Delta_{\lambda}$ both are non-analytic functions of the variable $\lambda$., Comment: 32 pages, several plots and figures; positivity condition added for Theorem on entanglement breaking channels; new result for entrywise positive channels