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The Rifle Barrel of Life: A Pure Hydrodynamic Mechanism for Chiral-Induced Spin Selectivity

Shichao Tang

Published Dec 21, 2025• 0 citations
Publisher

Abstract

The Chiral-Induced Spin Selectivity (CISS) effect—where electrons are filtered by their spin when passing through chiral molecules—presents a major puzzle in quantum biology. Conventional theories often rely on assumed strong internal electric fields. We propose a radical alternative based on Superfluid Vacuum Topological-Geometric Dynamics (SV-TGD): CISS is a macroscopic hydrodynamic sieving process. In this view, an electron is a microscopic vortex carrying circulation, and a chiral molecule acts as a "rifled barrel" that imposes a helical vortex field on the vacuum fluid. Spin-matched electrons flow smoothly; spin-mismatched ones are deflected by a transverse Magnus force. This purely mechanical picture yields testable predictions and stems from a deeper identity: the Lorentz force is mathematically equivalent to the Magnus force in a fluid vacuum.

DOI
10.5281/zenodo.18009652

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The Chiral-Induced Spin Selectivity (CISS) effect—where electrons are filtered by their spin when passing through chiral molecules—presents a major puzzle in quantum biology. Conventional theories often rely on assumed strong internal electric fields. We propose a radical alternative based on Superfluid Vacuum Topological-Geometric Dynamics (SV-TGD): CISS is a macroscopic hydrodynamic sieving process. In this view, an electron is a microscopic vortex carrying circulation, and a chiral molecule acts as a "rifled barrel" that imposes a helical vortex field on the vacuum fluid. Spin-matched electrons flow smoothly; spin-mismatched ones are deflected by a transverse Magnus force. This purely mechanical picture yields testable predictions and stems from a deeper identity: the Lorentz force is mathematically equivalent to the Magnus force in a fluid vacuum.
The chirality-induced spin selectivity (CISS) effect has been invoked to explain recent reports of differences in the time-resolved EPR signals between chiral and achiral molecules. However, the microscopic origin of these differences and their connection to CISS remains contested, particularly since these systems lack a metal interface. Here we introduce an intramolecular spinterface-like mechanism that naturally arises within donor-chiral bridge-acceptor (D--χχχB--A) complexes and quantitatively reproduces experimentally reported observed spin polarization in time-resolved EPR studies. In our two-electron Lindblad model, the photoexcited charge-transfer electron traversing the chiral bridge exchanges with the residual donor electron, which acts as a localized magnetic moment analogous to an induced magnetic moment on an electrode surface. The resulting through-bridge charge current produces an effective solenoidal field at the donor--bridge interface, breaking spin degeneracy and directional symmetry, thus enabling spin-selective transport without invoking intrinsic spin-orbit coupling on the bridge. We show that the interplay between this current-induced field, donor thermalization (which breaks time-reversal symmetry), and bridge spin mixing yields tens-of-percent polarization over realistic experimental conditions and charge-transfer time scales, matching reported CISS signatures in triads and DNA hairpins. By explicitly resolving the dependence on solenoidal coupling strength, temperature, and spin-mixing rates, the model identifies the regime in which internal spinterfaces can generate robust CISS-like spin filtering. These findings demonstrate that CISS-like signals in isolated D--χχχB--A complexes are fully compatible with a spinterface mechanism, providing a unified conceptual framework for interpreting both device-based and molecule-internal CISS platforms.
This work investigates the effect of chirality-induced spin selectivity (CISS) on quantum coherence in the radical-pair (RP) mechanism of avian magnetoreception. Additionally, we examine the correlation of global and local coherence measures with the yield of the signaling state in the RP model. We find that both relative entropy of global coherence and local coherence in the radical pair increase with CISS. However, only global coherence shows a strong correlation with the signaling state yield and thus indicates a plausible utilitarian role for the avian compass. We also analyze the interplay of dipolar and exchange interaction with the CISS and their effect on the coherence of the radical-pair spin. Further, we analyze the effect of environmental decoherence along with CISS. We conclude that a high CISS results in a high correlation of global coherence with signaling state yield. We propose that CISS might play an important role in developing quantum technologies by sustaining coherence in radical-pair-like quantum systems.
Chiral molecular structure can couple to electron spin, leading to unexpected spin polarization effects. This Chirality-Induced Spin Selectivity (CISS) was first reported for DNA molecules adsorbed on gold but its microscopic origin remains unclear. We demonstrated though simulation that the exchange arising from electron-electron Coulomb interactions within the self-consistent mean field (Hartree--Fock) approximation can yield significant (∼2%\sim 2\%∼2%) spin polarisation for 333-methylcyclohexanone adsorbed on Cu(111) amplifying a much smaller (∼0.0014%\sim 0.0014\%∼0.0014%) initial bias, consistent with experiment. Symmetry considerations ensure the result is physically meaningful, while its ab-initio nature ensures all parameters are physically realistic. This amplification is connected to existing studies on spin-symmetry breaking in Hartree--Fock, providing a new pathway for understanding the magnitude of CISS as an emergent phenomenon of interacting electrons.
The chirality-induced spin selectivity (CISS) effect, the coupling between structural chirality and electron spin polarization, has been experimentally observed across many diverse systems. However, despite extensive theoretical effort, a unified mechanistic understanding remains elusive. In this perspective, we demonstrate how some of the basic properties of the fascinating effects of CISS can be understood based on straightforward symmetry considerations commonly employed in fundamental particle physics. In particular, we show that CISS does not violate any fundamental symmetries including parity and time-reversal. By anchoring CISS within the universal language of symmetry, we offer a robust conceptual foundation for interpreting experiments and guiding future theoretical and experimental designs.
Whether chirality-induced spin selectivity (CISS) reflects coherent SU(2) spin rotation or incoherent spin-dependent filtering is a central unresolved question in molecular spintronics, with implications ranging from asymmetric chemistry to quantum information. We show that these two scenarios are distinguishable by a sharp symmetry criterion on the superexchange interaction mediated by a chiral molecular bridge. Coherent CISS, implemented as a unitary spin rotation of the tunneling electron, generates a giant Dzyaloshinskii-Moriya (DM) interaction with ratio |D|/JH up to 3, which is two orders of magnitude beyond intrinsic Rashba spin-orbit coupling in Si/SiGe. Incoherent CISS, represented by any Hermitian (non-unitary but spin-diagonal) tunneling matrix, produces D = 0 identically; we prove this as a structural theorem, reinforced by a Lindblad argument that dissipative spin filtering cannot modify virtual-tunneling-mediated superexchange. The DM interaction thus serves as a coherence order parameter, nonzero only when quantum amplitudes for opposite-spin transmission maintain a fixed relative phase. We derive closed-form angular, enantiomeric, and sensitivity signatures and show that the critical coherent rotation angle lies two orders of magnitude below current transport-inferred values and is accessible to existing 10 kHz exchange spectroscopy in gate-defined quantum dots. Five candidate molecules are predicted to exceed this threshold by one to two orders of magnitude even in a conservative interface-amplification scenario. The proposed measurement converts a long-standing transport controversy into a binary spin-qubit experiment with quantum-amplitude resolution.
Triplet formation and its regulation have always been of central interest in understanding the photophysical behavior of living systems. In organic systems, excessive triplet formation poses significant challenges, as it can promote photochemical damage and reduce the efficiency of charge separation processes, making its regulation critically important.Here, we present a theoretical investigation of the intrinsic quantum spin dynamics governing triplet formation in the heliobacterial reaction center, a system that operates without any internal magnetic field. Using an open quantum systems approach based on the Lindblad formalism, we simulate the spin-correlated radical pair dynamics occurring during charge separation in the heliobacterial reaction center. The study systematically examines how triplet formation is regulated by variations in two key parameters, hyperfine coupling strengths and recombination rates, and how this regulation is further influenced by the inclusion of chirality-induced spin selectivity (CISS) in conjunction with the radical pair mechanism (RPM). Our results demonstrate that the CISS effect significantly suppresses triplet formation across the parameter space relevant to the heliobacterial molecular environment, revealing an intrinsic quantum protective mechanism operating through spin control in heliobacterial photosynthesis.