“A bit of Quantum in Photosynthesis? Tracking Light-Harvesting on the nm & fs Scale”
Niek F. van Hulst

3 October at 12h 30
Sala de conferencias, módulo 0
Facultad de Ciencias – UAM

Nature has developed photosynthesis to power life. Quantum coherences have been observed in
the energy transfer of photosynthetic complexes, even at room temperature, hinting to a role of
deep physics in natural light harvesting. Does nature exploit quantum concepts? Does the coherence
help to find an optimal path for robust or efficient transfer? How are the coherences sustained?
What is their spatial extent in a real light-harvesting network?

Specializing on combining femtosecond spectroscopy with nanoscale microscopy, I aim to address
such questions by looking ultrafast into the nanoscale, to see biomolecules in action in a real system.
Indeed, addressing LH2 of purple bacteria, we revealed the first coherent oscillations of a single
photo-synthetic complex at physiological conditions, and even non-classical photon emission of the
multi-chromophoric LH2 complex.

In this INC Frontiers Colloquium first I’ll outline the methods to trace the fs coherences and energy
transfer of individual molecules, quantum dots and complexes. Single molecule detection generally
relies on detection of fluorescence, yet light harvesting complexes are designed for light transport,
not emission. Thus I will explore innovative alternatives: optical antennas to enhance quantum
efficiency; transient absorption on singles; detection of stimulated emission.

Imaging nanoscale light transport requires local excitation and detection far beyond the diffraction
limit. I’ll address the use of nanoholes and scanning resonant antenna probes to confine the light
field and couple effectively to single emitters on the nanoscale. The antenna acts as a nanocavity
with relative strong coupling (~100GHz), speeding up the radiative decay to picosecond time scale
and allowing > GHz single photon emission.

Finally combining both coherent fs excitation and localized nanoscale excitation/detection I will
explore potential quantum diffusion: the transport and extent of coherences throughout the lightharvesting membrane. I will conclude with an outlook of the challenges ahead and the perspectives of addressing coupled networks in real nano-space and on femtosecond timescale.