  The nature of excited states of open quantum systems produced by incoherent
natural thermal light is analyzed based on a description of the generator of
the dynamics. Natural thermal light is shown to generate long-lasting coherent
dynamics because of (i) the super-Ohmic character of the radiation, and (ii)
the absence of pure dephasing dynamics. In the presence of an environment, the
long-lasting coherences induced by suddenly turned-on incoherent light
dissipate and stationary coherences are established. As a particular
application, dynamics in a subunit of the PC-645 light-harvesting complex is
considered where it is further shown that aspects of the energy pathways
landscape depend on the nature of the exciting light and number of chromophores
excited. Specifically, pulsed laser and natural broadband incoherent excitation
induce significantly different energy transfer pathways. In addition, we
discuss differences in perspective associated with the eigenstate vs site
basis, and note an important difference in the phase of system coherences when
coupled to blackbody radiation or when coupled to a phonon background. Finally,
an Appendix contains an open systems example of the loss of coherence as the
turn on time of the light assumes natural time scales.
