Two-dimensional spectroscopy can distinguish between decoherence and dephasing of zero-quantum coherences

Andrew F. Fidler, Elad Harel, Phillip D. Long, Gregory S. Engel*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


Recent experiments on a variety of photosynthetic antenna systems have revealed that coherences among electronic states persist longer than previously anticipated. In an ensemble measurement, the observed dephasing of a coherent state can occur because of either disorder across the ensemble or decoherence from interactions with the bath. Distinguishing how much such disorder affects the experimentally observed dephasing rate is paramount for understanding the role that quantum coherence may play in energy transfer through these complexes. Here, we show that two-dimensional electronic spectra can distinguish between the limiting cases of homogeneous dephasing (decoherence) and inhomogeneous dephasing by examining how the quantum beat frequency changes within a cross peak. For the antenna complex LH2 isolated from Rhodobacter sphaeroides, we find that dephasing of the coherence between the B850 and B800 rings arises predominantly from inhomogeneity. In contrast, within the Fenna-Matthews-Olson (FMO) complex from Chlorobium tepidum, dephasing of the coherence between the first two excitons appears quite homogeneous. Thus, the observed dephasing rate sets an upper bound on decoherence for the LH2 complex while establishing both an upper and lower bound for the FMO complex.

Original languageEnglish (US)
Pages (from-to)282-289
Number of pages8
JournalJournal of Physical Chemistry A
Issue number1
StatePublished - Jan 12 2012

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry


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