In this Letter, we provide a model-independent method for ascertaining the number of parameters involved in complex quantum dynamics directly from experimental data. Our method exploits the linear independence of strings of input data. The novelty of this Letter is to render this method amenable to commonly employed pulsed techniques such as pump-probe spectroscopy and multi-dimensional electronic and vibrational spectroscopy.

We apply our method to experimental data from two ultrafast spectroscopy experiments from Spain and Sweden – both probing complex quantum dynamics in light harvesting complexes. For the frequently studied Fenna-Matthews-Olson complex, we identify the fewest number of real parameters necessary to explain the experimental data. Our model-independent conclusion is commensurate with a substantially more detailed model originally used in 2018. Our method also reveals a degree of excitonic localisation expected in this system.

While we illustrate our method for complex quantum dynamics of biomolecules, its general nature should make it applicable widely.