The Radical Pair Mechanism and the Avian Chemical Compass: Quantum Coherence and Entanglement

TL;DR

This paper reviews the radical pair mechanism as a quantum explanation for avian navigation, emphasizing the roles of quantum coherence and entanglement in the chemical compass within birds.

Contribution

It provides a comprehensive overview of the quantum radical pair mechanism and highlights the significance of quantum entanglement in avian magnetoreception under ambient conditions.

Findings

Quantum entanglement influences avian magnetic sensing.

The radical pair mechanism explains magnetic field effects on chemical reactions.

Quantum coherence persists at ambient conditions in biological systems.

Abstract

We review the spin radical pair mechanism which is a promising explanation of avian navigation. This mechanism is based on the dependence of product yields on (1) the hyperfine interaction involving electron spins and neighboring nuclear spins and (2) the intensity and orientation of the geomagnetic field. One surprising result is that even at ambient conditions quantum entanglement of electron spins can play an important role in avian magnetoreception. This review describes the general scheme of chemical reactions involving radical pairs generated from singlet and triplet precursors; the spin dynamics of the radical pairs; and the magnetic field dependence of product yields caused by the radical pair mechanism. The main part of the review includes a description of the chemical compass in birds. We review: the general properties of the avian compass; the basic scheme of the radical pair mechanism; the reaction kinetics in cryptochrome; quantum coherence and entanglement in the avian compass; and the effects of noise. We believe that the "quantum avian compass" can play an important role in avian navigation and can also provide the foundation for a new generation of sensitive and selective magnetic-sensing nano-devices.