Interradical motion can push magnetosensing precision toward quantum limits

Magnetosensitive spin-correlated radical pairs offer a promising platform for noise-robust quantum metrology; however, unavoidable interradical interactions, such as electron-electron dipolar and exchange couplings, alongside deleterious perturbations resulting from intrinsic radical motion, typically degrade their potential as magnetometers. In contrast, we show how structured molecular motion modulating interradical interactions in a chemical sensor in cryptochrome can, in fact, increase sensitivity and, moreover, push precision in estimating magnetic field directions closer to the quantum Cramér-Rao bound. The latter is evident both on average over the magnetoreceptor array and, to an even greater extent, for the subset of best-performing magnetoreceptors, thus suggesting near-optimal metrological performance. Remarkably, this approach to optimality is amplified under environmental noise and persists with increasing complexity of the spin system, suggesting that perturbations inherent to such natural systems have enabled them to operate closer to the quantum limit to more effectively extract information from the weak geomagnetic field. This insight opens the possibility of channeling the underlying physical principles of motion-induced modulation of electron spin-spin interactions toward devising efficient handles over emerging molecular quantum information technologies.