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The Quantum Lens: Noise-Assisted Sensitivity in Avian Magnetoreception

Ciann-Dong Yang, Wei‐Ju Chen

Published Sep 9, 2026• 0 citations
Publisher

Abstract

Abstract Avian magnetoreception based on the radical-pair mechanism explains how migratory birds navigate using the geomagnetic field. However, how these microscopic quantum states persist against environmental noise in vivo remains a fundamental challenge. We address this by presenting a scalable vectorized state-space framework of open quantum dynamics under decoherence, universally applicable to arbitrary n-particle spin-coupled systems. By vectorizing the density matrix in the Lindblad master equation, we map the spin dynamics from Hilbert to Liouville space, bypassing traditional numerical bottlenecks. Crucially, leveraging initial singlet-state constraints reduces the active decoherence operators from 64 to 16, significantly accelerating open-system simulations. Projecting triplet yields onto a virtual retina model reveals that environmental noise exerts dual, pathway-dependent effects on navigation accuracy. While singlet–singlet relaxation (\(\:SS\)) and longitudinal phase dephasing (\(\:S{T}_{0}\)) degrade sensitivity through contrast washout, transverse phase dephasing (\(\:S{T}_{\pm\:}\)) acts counterintuitively as a "quantum lens". This transverse channel filters off-axis noise, concentrating triplet yields at the retinal center to enhance magnetic sensitivity by 35.2%. These findings demonstrate that environmental noise can be constructively harnessed, offering a new design paradigm for noise-tolerant, high-precision bionic quantum compasses.

DOI
10.21203/rs.3.rs-10851803/v1

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•Nov 27, 2025•0 citations
Abstract Avian magnetoreception based on the radical-pair mechanism explains how migratory birds navigate using the geomagnetic field. However, how these microscopic quantum states persist against environmental noise in vivo remains a fundamental challenge. We address this by presenting a scalable vectorized state-space framework of open quantum dynamics under decoherence, universally applicable to arbitrary n-particle spin-coupled systems. By vectorizing the density matrix in the Lindblad master equation, we map the spin dynamics from Hilbert to Liouville space, bypassing traditional numerical bottlenecks. Crucially, leveraging initial singlet-state constraints reduces the active decoherence operators from 64 to 16, significantly accelerating open-system simulations. Projecting triplet yields onto a virtual retina model reveals that environmental noise exerts dual, pathway-dependent effects on navigation accuracy. While singlet–singlet relaxation ((:SS)) and longitudinal phase dephasing ((:S{T}{0})) degrade sensitivity through contrast washout, transverse phase dephasing ((:S{T}{\pm:})) acts counterintuitively as a "quantum lens". This transverse channel filters off-axis noise, concentrating triplet yields at the retinal center to enhance magnetic sensitivity by 35.2%. These findings demonstrate that environmental noise can be constructively harnessed, offering a new design paradigm for noise-tolerant, high-precision bionic quantum compasses.
Quantum computing applications in diverse domains are emerging rapidly. Given the limitations of classical computing techniques, the peculiarity of quantum circuits, which can observe quantum phenomena such as superposition, entanglement, and quantum coherence, is remarkable. This capability enables them to achieve measurement sensitivities far beyond classical limits. Research on radical pair-based magnetoreception in migratory birds has been a focus area for quite some time. A quantum mechanics-based computing approach, thus unsurprisingly, identifies a scope of application. In this study, to observe the phenomenon, electron-nucleus spin quantum circuits for different geomagnetic fluxes have been simulated and run through IBM Qiskit quantum processing units with error mitigation techniques. The results of different quantum states are consistent, suggesting singlet-triplet mechanisms that can be emulated, resembling the environment-enabling flights of migratory birds through generations of the avian species. The four-qubit model emulating electron-nucleus systems mimicking the environmental complexity outcome shows the sensitiveness to change of magnetic flux index, high probability of singlet-triplet dynamics, and upholding radical pair model states by the purity of the sub-system and full system outcome of coherence, the hallmark of singlet state dominance. The work involved performing fifty quantum circuits for different magnetic field values, each with one thousand and twenty-four shots for measurement, either in the simulator or on real quantum hardware, and for two error mitigation techniques, preceded by a noise model of a simulator run.
The radical pair (RP) mechanism, which describes the quantum dynamics of a spatially separated electron pair, is considered as one of the principal models of avian magnetoreception. Different from the conventional phenomenological approach where the sensitivity of avian magnetoreception is characterized by the singlet yield ΦSΦ_{S}ΦS​, we introduce the quantum Fisher information (QFI), which represents the maximum information about the magnetic field's direction extracted from the RP state, to give a precise measure of sensitivity of avian compass essentially. The consistency between our results and experimental observations suggests that QFI plays a decisive role in avian magnetoreception. Besides, within the framework of quantum metrology, we can judge the feasibility of any possible measurement scheme for avian magnetoreception, and shed light on an intrinsic relevance between the singlet yield and a concrete measurement scheme of our approach. The present work allows us to understand many things about avian magnetoreception from a fully new perspective of quantum metrology, and provide a new route to establish a direct connection between quantum information and many other biological functions.
Migratory birds detect the Earth’s magnetic field with remarkable precision using a quantum process in retinal cryptochrome proteins. We review the observational and experimental evidence supporting the radical-pair mechanism and propose a simple dynamical model that augments the standard radical-pair Hamiltonian with a minimal geometric protection term. This term is modulated by consecutive Fibonacci numbers whose ratios converge to the golden ratio ϕ = (1 + √5)/2 ≈ 1.618. Numerical integration and analytical fixed-point analysis show that the protection term naturally stabilizes singlet–triplet coherence lifetimes and optimizes magnetic sensitivity at geomagnetic field strengths and inclinations observed in nature. The model is fully classical, self-contained, and provides a new quantitative explanation for the robustness of avian magnetoreception. It offers the first empirical hint of a universal geometric principle governing quantum coherence in biological systems.
It is known that more than 50 species use the Earth's magnetic field for orientation and navigation. Intensive studies, particularly behavior experiments with birds, provide support for a chemical compass based on magnetically sensitive free radical reactions as a source of this sense. However, the fundamental question of how quantum coherence plays an essential role in such a chemical compass model of avian magnetoreception yet remains controversial. Here, we show that the essence of the chemical compass model can be understood in analogy to a quantum interferometer exploiting global quantum coherence rather than any subsystem coherence. Within the framework of quantum metrology, we quantify global quantum coherence and correlate it with the function of chemical magnetoreception. Our results allow us to understand and predict how various factors can affect the performance of a chemical compass from the unique perspective of quantum coherence assisted metrology. This represents a crucial step to affirm a direct connection between quantum coherence and the function of a chemical compass.
The radical pair model has been successful in explaining behavioral characteristics of the geomagnetic compass believed to underlie the navigation capability of certain avian species. In this study, the spin dynamics of the radical pair model and decoherence therein are interpreted from a microscopic state transition point of view. This helps to elucidate the interplay between the hyperfine and Zeeman interactions that enables the avian compass and clarify the distinctive effects of nuclear and environmental decoherence on it. Three regimes have been identified for the strength of the hyperfine interaction with respect to that of the geomagnetic Zeeman. It is found that the compass is likely to function in the large hyperfine interaction regime. Using a quantum information theoretic quantifier of coherence, we find that nuclear decoherence induces new structure in the spin dynamics for intermediate hyperfine interaction strength. On the other hand, environmental decoherence-modeled by two different noise models-seems to disrupt the compass action.
The quantum control of spin-correlated radical pairs (SCRPs) holds promise for the targeted manipulation of magnetic field effects (MFEs), with potential applications ranging from the design of noise-resilient quantum information processors to genetically encodable quantum sensors. However, achieving precise handles over the intricate interplay between coherent electron spin dynamics and incoherent relaxation processes in photo-excited radical-pair reactions requires tractable approaches for numerically obtaining controls for large, complex open quantum systems. To that end, we realise optimal control of SCRPs in the low-magnetic-field regime, through first generalising the gradient-ascent pulse engineering (GRAPE) paradigm to allow for optimising time-integral reaction yields for coherent control of SCRP spin dynamics. We then explore how interradical interactions which are unavoidable in a biophysical setting, such as electron-electron dipolar and exchange couplings, alongside driving resulting from intrinsic structural motion, can push the precision of the proposed radical pair quantum compass in cryptochrome closer to approaching the quantum Cram\'{e}r-Rao bound. 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. Bolstered by these findings, we furthermore demonstrate how a control engineering approach based on the Pontryagin Maximum Principle (PMP) can offer a more computationally feasible route towards realising not only coherent, but also incoherent control, of noisy SCRP open-system spin dynamics. This raises prospects for experimental realisation of spin control of actual radical-pair systems in ambient magnetic fields, by suppressing or boosting radical reaction yields using purpose-specific radio-frequency wave forms, paving the way for inspiring more noise-robust quantum magnetometry via chemical reaction-yield-dependence, and potentially applications of quantum control to physiologically relevant radical-pair reaction intermediates.