Quantum dynamics of the avian compass

TL;DR

This paper models the quantum spin dynamics involved in the avian magnetic compass, demonstrating millisecond coherence times that support the hypothesis of quantum coherence in bird navigation.

Contribution

It provides a detailed theoretical analysis of decoherence mechanisms in radical pair models, explaining how coherence is maintained in biological magnetic sensing.

Findings

Decoherence rates are consistent with millisecond coherence times.

Hyperfine interactions cause dephasing but still allow for magnetic field sensing.

The model aligns with behavioral experiments on bird navigation.

Abstract

The ability of migratory birds to orient relative to the Earth's magnetic field is believed to involve a coherent superposition of two spin states of a radical electron pair. However, the mechanism by which this coherence can be maintained in the face of strong interactions with the cellular environment has remained unclear. This Letter addresses the problem of decoherence between two electron spins due to hyperfine interaction with a bath of spin 1/2 nuclei. Dynamics of the radical pair density matrix are derived and shown to yield a simple mechanism for sensing magnetic field orientation. Rates of dephasing and decoherence are calculated ab initio and found to yield millisecond coherence times, consistent with behavioral experiments.