The quantum Goldilocks effect: on the convergence of timescales in quantum transport

TL;DR

This paper introduces the quantum Goldilocks effect, explaining how natural selection optimizes quantum coherence in photosynthesis to achieve efficient energy transport across diverse timescales.

Contribution

It presents a general theory linking quantum coherence levels to optimal transport efficiency, governed by a single parameter, illustrating a natural selection mechanism.

Findings

Convergence of timescales in photosynthesis explained as a quantum Goldilocks effect.

A unified parameter governs optimal quantum transport efficiency.

Natural selection drives quantum systems toward 'just right' coherence levels.

Abstract

Excitonic transport in photosynthesis exhibits a wide range of time scales. Absorption and initial relaxation takes place over tens of femtoseconds. Excitonic lifetimes are on the order of a nanosecond. Hopping rates, energy differences between chromophores, reorganization energies, and decoherence rates correspond to time scales on the order of picoseconds. The functional nature of the divergence of time scales is easily understood: strong coupling to the electromagnetic field over a broad band of frequencies yields rapid absorption, while long excitonic lifetimes increase the amount of energy that makes its way to the reaction center to be converted to chemical energy. The convergence of the remaining time scales to the centerpoint of the overall temporal range is harder to understand. In this paper we argue that the convergence of timescales in photosynthesis can be understood as an example of the `quantum Goldilocks effect': natural selection tends to drive quantum systems to the degree of quantum coherence that is `just right' for attaining maximum efficiency. We provide a general theory of optimal and robust, efficient transport in quantum systems, and show that it is governed by a single parameter.