The quantum Zeno effect immunizes the avian compass against the deleterious effects of exchange and dipolar interactions

Abstract

Magnetic-sensitive radical-ion-pair reactions are understood to underlie the biochemical magnetic compass used by avian species for navigation. Recent experiments have provided growing evidence for the radical-ion-pair magnetoreception mechanism, while recent theoretical advances have unravelled the quantum nature of radical-ion-pair reactions, which were shown to manifest a host of quantum-information-science concepts and effects, like quantum measurement, quantum jumps and the quantum Zeno effect. We here show that the quantum Zeno effect provides for the robustness of the avian compass mechanism, and immunizes its magnetic and angular sensitivity against the deleterious and molecule-specific exchange and dipolar interactions.

Magnetic orientation of garden warblers ( Sylvia borin ) under 1.4 MHz radiofrequency magnetic field

“…No need to say that any remotely realistic model of the radical pair would give worse sensitivity to the RF field than the 'reference -probe' model considered above. Several theoretical works published in recent years have attempted to reproduce some of the experimental results [28][29][30], invoking various quantum and statistical effects to suppress decoherence and enhance sensitivity. With rather liberal choice of relaxation times, the effect of a strictly resonant RF field with the amplitude of 150 nT could be reproduced [28].…”

The quantum needle of the avian magnetic compass

“…In support of this proposal, the photochemistry of isolated cryptochromes in vitro has been found to respond to applied magnetic fields in a manner that is quantitatively consistent with the radical pair mechanism (15). Aspects of the radical pair hypothesis have also been explored in a number of theoretical studies, the majority of which have concentrated on the magnitude of the anisotropic magnetic field effect (9,10,16,17,(19)(20)(21)(22)(23)(24)(25)(26)(27). Very little attention has been devoted to the matter we address here: the precision of the compass bearing available from a radical pair sensor (28).…”

“…A crucial element in all such calculations is the presence of nuclear spins whose hyperfine interactions are the source of the magnetic anisotropy (8,16). Most studies have focused on idealized spin systems comprising the two electron spins, one on each radical, augmented by one or two nuclear spins (9,(21)(22)(23)(24)(25)(26)(27)34). Only a handful has attempted to deal with realistic, multinuclear radical pairs (10,16,17,20).…”

“…Several studies have assumed, explicitly or implicitly, that the spin coherence persists for about a microsecond, i.e., the reciprocal of the electron Larmor frequency (1.4 MHz) in a 50-μT field (9,10,17,20). Either because the spin system was grossly oversimplified (9,(21)(22)(23)(24)(25)(26)(27)34), or because of this restriction on the spin coherence time, previous theoretical treatments have generally predicted the reaction yield to be a gently varying (often approximately sinusoidal) function of the orientation of the radical pair in the geomagnetic field. Although capable of delivering information on the direction of the field, such a compass would not provide a precise heading.…”

Quantum dynamics of the avian compass

“…Although arising from a different source, this dynamics is similar to the quantum Zeno regime treated in [24,27], where fast singlet or triplet reaction rates take the place of rapid dephasing, and to [40], where the long-lived coherences occur in photosynthetic molecules. Because the z component of the Bloch vector decays rapidly, the symmetry group of the longlived information is U(1) rather than SU (2).…”