Abstract Quantum biology has identified nontrivial quantum effects in living systems, yet how quantum dynamics are converted into robust biological function under physiological noise remains unclear. We argue that the key challenge is transduction—how quantum dynamics produce stable biological outputs—rather than coherence preservation. Using radical pair magnetoreception as a model system, we find a pronounced response plateau in magnetic anisotropy as a function of the recombination-rate ratio, robust across modelling choices and absolute rate scaling, while disappearing under hyperfine ablation. Moderate dephasing enhances the response within a bounded noise window, offering a natural account of the mismatch between in vivo robustness and in vitro fragility. Spectral analysis identifies mode identity exchange as a signature of the plateau boundary. A minimal open-quantum toy model reproduces the key qualitative features, suggesting broader applicability. Together, these results support a view of quantum-to-biological transduction as a problem of regime stability rather than signal optimisation.
Abstract Quantum biology has identified nontrivial quantum effects in living systems, yet how quantum dynamics are converted into robust biological function under physiological noise remains unclear. We argue that the key challenge is transduction—how quantum dynamics produce stable biological outputs—rather than coherence preservation. Using radical pair magnetoreception as a model system, we find a pronounced response plateau in magnetic anisotropy as a function of the recombination-rate ratio, robust across modelling choices and absolute rate scaling, while disappearing under hyperfine ablation. Moderate dephasing enhances the response within a bounded noise window, offering a natural account of the mismatch between in vivo robustness and in vitro fragility. Spectral analysis identifies mode identity exchange as a signature of the plateau boundary. A minimal open-quantum toy model reproduces the key qualitative features, suggesting broader applicability. Together, these results support a view of quantum-to-biological transduction as a problem of regime stability rather than signal optimisation.
Broad response regions in a reaction-rate ratio do not by themselves identify a biological transduction mechanism. This correction audits the earlier quantum-biological transduction preprint, distinguishes its original and later model versions, and checks selected outputs from a related corrected radical-pair study. Nondimensionalization and explicit two-point error bounds show why a fixed recombination-rate ratio does not generally preserve the absolute response when magnetic frequencies remain fixed. A classical two-stage success probability has a broad interior peak and exact rate-scale invariance; this establishes the non-specificity of curve shape, without reproducing magnetic anisotropy. The earlier pumped two-level model also lacks a specified finite readout: its unweighted population integral diverges when its stationary excited population is positive. Reaction generators, normalization, environmental channels and spectral overlap weights therefore require explicit treatment. Original figure producers and the advertised later source archive remain unrecovered. The numerical examples are attributed, known-target secondary evidence; no new spin simulation or biological experiment is reported. Claims of general formalism robustness, isotope catastrophe, cross-species ratio invariance and a physiological explanation are withdrawn. The retained contribution is an auditable correction and a set of model-comparison requirements. A matched-observable mechanism test and a demonstrated biological pathway remain absent. Corrective release containing the revised manuscript and audit supplement. Related Research Square record: https://www.researchsquare.com/article/rs-8800376 . Earlier unsupported interpretations are withdrawn as detailed in the manuscript. This preprint is not peer reviewed.
This work presents a rigorous, cross-domain review of mechanisms in living systems that exhibit mathematical parallels with quantum error correction (QEC). Rather than relying on metaphor or loose analogy, the paper traces concrete isomorphisms between stabilizer codes, decoherence-free subspaces, dynamical decoupling, and the specific molecular architectures that sustain high-fidelity biological information. The review synthesizes evidence across three domains—genomic stability, neural information processing, and metabolic coherence—and examines proton tunneling, tautomer suppression, nuclear spin protection, microtubule lattice codes, excitonic transport, ENAQT, vibronic stabilizers, and the radical-pair magnetoreception model. By comparing these biological processes to formal properties of QEC (Knill–Laflamme conditions, threshold theorems, syndrome extraction, and topological protection), the work argues that biological robustness can be understood as an evolved form of error-correcting architecture. The conclusion highlights the role of noise-structured environments, energetic cost constraints, and threshold behavior, and proposes that QEC-style mechanisms may be universal to life operating near the quantum–classical boundary.
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.
Abstract Organisms continually commit to actions and occasionally cancel them before they occur. Whether quantum coherence could shape such decisions is debated, and the proposed radical-pair substrate in the brain has been read optimistically: biological noise was treated as a computational resource, coherence times as milliseconds, and error-corrected coherence as preserved deliberation. However, each of these readings is, on inspection, the opposite of what a careful open-systems analysis gives. Here we study the three-layer radical-pair hypothesis under a single revised theory anchored on cryptochrome, importing two established physics tools—open-system quantum error correction and the drift-to-bound theory of decisions—into the living-decision problem. We show that at biological rates the radical-pair channel is entanglement-breaking, that motional narrowing (protein tumbling acting as natural dynamical decoupling) is what restores a correctable regime, and that decoherence-free encoding with concatenation then reaches fidelity F = 0.996. Used as a reservoir, the system gives no advantage for static classification but a temporal-prediction error that tracks quantum resources (rQFI = −0.52). Strikingly, when the reservoir drives a decision, error correction does not enlarge the window in which the action can be vetoed; by preserving the decision signal it reaches the motor threshold sooner and advances the point of no return toward the action, a result we reproduce as a fidelity rescue on IBM superconducting hardware (an analog of the mechanism, not of the biology). We distill this into the principle of error-correction–advanced commitment: a more coherent decision is faster and less revisable, not freer—sharpening, rather than resolving, the question of quantum agency.
Abstract Quantum sensing enables the ultimate precision attainable in parameter estimation. Circumstantial evidence suggests that certain organisms, most notably migratory songbirds, also harness quantum-enhanced magnetic field sensing via a radical-pair-based chemical compass for the precise detection of the weak geomagnetic field. However, what underpins the acuity of such a compass operating in a noisy biological setting, at physiological temperatures, remains an open question. Here, we address the fundamental limits of inferring geomagnetic field directions from radical-pair spin dynamics. Specifically, we compare the compass precision, as derived from the directional dependence of the radical-pair recombination yield, to the ultimate precision potentially realisable by a quantum measurement on the spin system under steady-state conditions. To this end, we probe the quantum Fisher information and associated Cramér–Rao bound in spin models of realistic complexity, accounting for complex inter-radical interactions, a multitude of hyperfine couplings, and asymmetric recombination kinetics, as characteristic for the magnetosensory protein cryptochrome. We compare several models implicated in cryptochrome magnetoreception and unveil their optimality through the precision of measurements ostensibly accessible to nature. Overall, the comparison provides insight into processes honed by nature to realise optimality whilst constrained to operating with mere reaction yields. Generally, the inference of compass orientation from recombination yields approaches optimality in the limits of complexity, yet levels off short of the theoretical optimal precision bounds by up to one or two orders of magnitude, thus underscoring the potential for improving on design principles inherent to natural systems.
Living systems operate far from thermodynamic equilibrium while maintaining a high degree of internal order, raising the long-standing question of how fragile quantum coherence can persist in warm, noisy biological environments. While several biological processes exhibit signatures of quantum coherence, the physical mechanisms responsible for stabilizing such coherence remain an active area of debate. In this work, we present a phenomenological model demonstrating that quantum coherence in open spin systems can be stabilized through entropy-dependent feedback with a weakly coupled coherent field. We consider an open quantum spin ensemble subject to environmental decoherence, augmented by (i) entropy-sensitive suppression of decoherence and (ii) a coherence-inducing interaction that favors low-entropy, collectively coherent configurations. Using multipartite Greenberger-Horne-Zeilinger (GHZ) states as representative low-entropy coherent states, numerical simulations reveal nonlinear threshold behavior, entropy collapse, and long-lived coherence despite strong environmental noise. These features provide clear signatures of a positive feedback loop, wherein coherence suppresses decoherence, reduced decoherence enhances coherence, and the resulting self-reinforcement stabilizes the system. Importantly, the model is agnostic to the physical origin of the coherent field and is compatible with a wide range of candidates, including internally generated biological oscillations, collective electromagnetic or redox dynamics, oxygen-mediated spin correlations, and other structured cellular fields. As an illustrative example, we discuss the potential role of an ultralight dark matter (ULDM) background field, whose predicted macroscopic coherence and oscillation frequencies could, in principle, participate in the same feedback mechanism. By separating the general principle of feedback-stabilized coherence from any specific physical realization, this work provides a unifying theoretical framework for understanding how quantum coherence may persist in open, noisy systems relevant to biological physics. The results suggest that coherence in living matter may arise not from isolation from the environment, but from structured coupling to coherent fields that dynamically regulate decoherence through entropy-sensitive feedback.