title: Practical witness for electronic coherences.
abstract: The origin of the coherences in two-dimensional spectroscopy of photosynthetic complexes remains disputed. Recently, it has been shown that in the ultrashort-pulse limit, oscillations in a frequency-integrated pump-probe signal correspond exclusively to electronic coherences, and thus such experiments can be used to form a test for electronic vs. vibrational oscillations in such systems. Here, we demonstrate a method for practically implementing such a test, whereby pump-probe signals are taken at several different pulse durations and used to extrapolate to the ultrashort-pulse limit. We present analytic and numerical results determining requirements for pulse durations and the optimal choice of pulse central frequency, which can be determined from an absorption spectrum. Our results suggest that for numerous systems, the required experiment could be implemented by many ultrafast spectroscopy laboratories using pulses of tens of femtoseconds in duration. Such experiments could resolve the standing debate over the nature of coherences in photosynthetic complexes.
authors.affiliation: Department of Physics, University of Ottawa, Ottawa K1N 6N5, Canada.
authors.forename: Allan S
authors.initials: AS
authors.lastname: Johnson
authors.affiliation: Center for Excitonics, Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Joel
authors.initials: J
authors.lastname: Yuen-Zhou
authors.affiliation: Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Alán
authors.initials: A
authors.lastname: Aspuru-Guzik
authors.affiliation: Department of Physics, University of Ottawa, Ottawa K1N 6N5, Canada.
authors.forename: Jacob J
authors.initials: JJ
authors.lastname: Krich
mesh_terms: D003198:Computer Simulation; D019281:Dimerization; D055590:Electromagnetic Phenomena; D008956:Models, Chemical; D013057:Spectrum Analysis; D014732:Vibration