07/11/2014, 14:00 — 15:00 — Room P9, Mathematics Building
Niek van Hulst, ICFO – The Institute of Photonic Sciences
A bit a of quantum in bacterial photosynthetic complexes
I will address the role of quantum effects in photosynthesis. Exploring individual pigment-protein complexes (LH2) of a purple bacterium with coherent fs pulses it is observed that ultrafast quantum coherent energy transfer occurs under physiological conditions. Surprisingly quantum coherences between electronically coupled energy eigen-states persist at least 400 fs, and distinct, time-varying energy transfer pathways can be identified in each complex. Interestingly the single molecule approach allows to track coherent phase jumps between different pathways, which suggest that long-lived quantum coherence renders energy transfer robust in the presence of disorder.
The photosynthetic antenna complexes are efficient in energy transfer, yet such complexes are not designed to emit light and thus hard to observe at the level of individual units. We have developed nanofabrication methods to couple single pigment complexes resonantly to a gold nanoantenna. This way the fluorescence decay speeds up from nanosecond to picosecond timescale, the quantum efficiency is enhanced and up to 1000 times more emission is collected. Using the bright photon emission, we revealed that the bacterial LH2 complex with 27 bacteriochlorophylls coordinated in two rings of chromophores shows photon anti-bunching at ambient conditions, i.e. a bacterial complex acting as a non-classical single-photon emitter.