Ion channels in cell membranes pass specific ions at rates approaching 10^8 per second while rejecting chemically similar ions almost completely. Potassium channels pass potassium and reject sodium; sodium channels do the reverse. The selectivity filter — a narrow region of the channel just a few angstroms wide — imposes this specificity through coordinated binding sites that match the target ion's size and charge distribution.
The paradox is that selectivity implies tight binding, and tight binding implies slow release. An ion held firmly enough to be distinguished from a slightly smaller competitor should not leave the binding site 100 million times per second. Classical molecular dynamics and Poisson-Nernst-Planck electrodiffusion models both struggle with this: they can reproduce selectivity or high flux, but consistently underestimate single-channel conductance when both constraints are applied simultaneously.
Zhou, Li, Zhang, Huang, Xiang, and Chang (arXiv:2603.07196, March 2026) propose that quantum tunneling resolves the paradox. Using a non-perturbative quantum transport framework — treating the selectivity filter as a mesoscopic conductor and computing ion transmission through a transfer matrix formalism — they show that ions tunnel through the energy barriers between binding sites rather than thermally climbing over them. Classical transport requires ions to acquire enough thermal energy to surmount each barrier (Arrhenius activation). Quantum transport allows ions to traverse barriers that are too tall for thermal activation at physiological temperatures.
The quantum model quantitatively recovers experimental conductance values for both Na+ and K+ channels — the values that classical models systematically underestimate. The claim is strong: quantum mechanics is not an exotic correction to classical ion transport. It is a fundamental prerequisite for achieving the conductance that cells require. Without tunneling, the selectivity filter would be too slow.
The model predicts transport resonances in the terahertz regime — specific frequencies at which the quantum transmission through the filter peaks. These are testable: terahertz spectroscopy of ion channels should reveal signatures that classical models cannot produce. Whether the prediction survives experimental test will determine whether this framework transforms quantum biology or joins the list of provocative proposals that didn't replicate.
Zhou, Li, Zhang, Huang, Xiang, and Chang, "Quantum Tunneling Enables High-Flux Transport in Ion Channels," arXiv:2603.07196 (March 2026).