Long-lived quantum coherence in photosynthetic complexes at physiological temperature

TLDR

Photosynthetic antenna complexes capture solar radiation and transfer excitation to reaction centers with near‑perfect quantum efficiency, and recent cryogenic experiments have shown coherent, wave‑like energy transfer in pigment‑protein complexes, a phenomenon that theory predicts should persist at physiological temperatures but has not yet been observed in FMO. The authors model the Fenna–Matthews–Olson complex, showing that environmentally assisted quantum transfer efficiency peaks at physiological temperatures and is enhanced by correlated protein motions that stabilize the energy landscape and protect coherence across a wide temperature range. Experimental data show that quantum coherence in FMO persists for at least 300 fs at physiological temperature, confirming that the wave‑like energy transfer observed at 77 K operates in vivo and that protein‑mediated correlated motions preserve coherence across 77 K to 277 K.

Abstract

Photosynthetic antenna complexes capture and concentrate solar radiation by transferring the excitation to the reaction center that stores energy from the photon in chemical bonds. This process occurs with near-perfect quantum efficiency. Recent experiments at cryogenic temperatures have revealed that coherent energy transfer—a wave-like transfer mechanism—occurs in many photosynthetic pigment-protein complexes. Using the Fenna–Matthews–Olson antenna complex (FMO) as a model system, theoretical studies incorporating both incoherent and coherent transfer as well as thermal dephasing predict that environmentally assisted quantum transfer efficiency peaks near physiological temperature; these studies also show that this mechanism simultaneously improves the robustness of the energy transfer process. This theory requires long-lived quantum coherence at room temperature, which never has been observed in FMO. Here we present evidence that quantum coherence survives in FMO at physiological temperature for at least 300 fs, long enough to impact biological energy transport. These data prove that the wave-like energy transfer process discovered at 77 K is directly relevant to biological function. Microscopically, we attribute this long coherence lifetime to correlated motions within the protein matrix encapsulating the chromophores, and we find that the degree of protection afforded by the protein appears constant between 77 K and 277 K. The protein shapes the energy landscape and mediates an efficient energy transfer despite thermal fluctuations.