Limits of quantum speedup in photosynthetic light harvesting

TL;DR

This paper investigates the potential for quantum speedup in photosynthetic light harvesting, revealing that such speedups are short-lived and that biological systems prioritize efficiency and robustness over quantum acceleration.

Contribution

The study compares light harvesting dynamics to quantum walks, demonstrating the limited and transient nature of quantum speedup in biological systems.

Findings

Quantum speedup in FMO complex lasts only about 70 fs

Quantum coherence persists for longer than the speedup duration

Light-harvesting complexes favor efficiency over quantum speedup

Abstract

It has been suggested that excitation transport in photosynthetic light harvesting complexes features speedups analogous to those found in quantum algorithms. Here we compare the dynamics in these light harvesting systems to the dynamics of quantum walks, in order to elucidate the limits of such quantum speedups. For the Fenna-Matthews-Olson (FMO) complex of green sulfur bacteria, we show that while there is indeed speedup at short times, this is short lived (70 fs) despite longer lived (ps) quantum coherence. Remarkably, this time scale is independent of the details of the decoherence model. More generally, we show that the distinguishing features of light-harvesting complexes not only limit the extent of quantum speedup but also reduce rates of diffusive transport. These results suggest that quantum coherent effects in biological systems are optimized for efficiency or robustness rather than the more elusive goal of quantum speedup.