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Stronger Nearest-Neighbor Coupling Amplifies Transient Pairwise Entanglement in Noisy Open Quantum Spin Chains: A Minimal Model

Ngo Cheung

Published Apr 11, 2026• 0 citations
Publisher

Abstract

Quantum entanglement usually vanishes almost instantly in warm, noisy environments, which is why many researchers have long dismissed its relevance to biology. Yet our simulations of a minimal four-qubit XXZ spin chain under realistic finite-temperature dissipation show something surprising: stronger nearest-neighbor coupling can dramatically amplify the transient peak of pairwise entanglement before the system thermalizes.Increasing the coupling strength J from 0.5 to 8.0 raised the maximum concurrence from 0.1103 to 0.4368, with parallel gains in negativity and quantum mutual information. Remarkably, the late-time global purity always settled at the same value (0.1397) regardless of J. A classical Kuramoto oscillator model displayed qualitatively identical coupling-dependent improvement, indicating the effect is not uniquely quantum.These Level-A results demonstrate that stronger interactions can act as a transient entanglement amplifier in dissipative spin networks. Any possible connection to microtubules or brain processes remains strictly hypothetical.

DOI
10.6084/m9.figshare.31987449

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Abstract The pairwise entanglement of the Heisenberg XX chain with next-nearest-neighbor (NNN) interac-tions was investigated by using the concurrence measure. The results show that for the nearest-neighbor sites,the entanglement may be improved or suppressed depending on the magnitudes of the NNN coupling constant J , while for the next-nearest-neighbor sites, it always increases with the increase of jJj . The critical tempera-ture T c decreases with the increase of J for the nearest-neighbor entanglement and increases with the increaseof jJj for the next-nearest-neighbor entanglement, respectively. We also show that the general Heisenberg XXmodel still can be used to create the entangled W states of three and four qubits, and that the presence ofNNN coupling has no efiect on the creation of four-qubit W states, while it shifts the instant of time at whichthe three-qubit W states are created.Key words Heisenberg XX chain, next-nearest-neighbor interaction, thermal entanglement 1 Introduction

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Quantum entanglement usually vanishes almost instantly in warm, noisy environments, which is why many researchers have long dismissed its relevance to biology. Yet our simulations of a minimal four-qubit XXZ spin chain under realistic finite-temperature dissipation show something surprising: stronger nearest-neighbor coupling can dramatically amplify the transient peak of pairwise entanglement before the system thermalizes.Increasing the coupling strength J from 0.5 to 8.0 raised the maximum concurrence from 0.1103 to 0.4368, with parallel gains in negativity and quantum mutual information. Remarkably, the late-time global purity always settled at the same value (0.1397) regardless of J. A classical Kuramoto oscillator model displayed qualitatively identical coupling-dependent improvement, indicating the effect is not uniquely quantum.These Level-A results demonstrate that stronger interactions can act as a transient entanglement amplifier in dissipative spin networks. Any possible connection to microtubules or brain processes remains strictly hypothetical.
We developed a minimal open-quantum-systems pipeline in QuTiP to examine how nearest-neighbor coupling, lattice topology, and multilayer bath structure shape transient entanglement and coherence lifetime in finite XXZ spin chains. The model used N = 4 to 6 qubits evolving under the Lindblad master equation from a product coherent initial state. Four topologies were tested—chain, ring, ladder, and helical_segment—together with five bath variants: local Markovian, Trp_collective, correlated dephasing, non-Markovian memory kernel, and a full combination of all bath layers. Coupling strength J was swept systematically.Across all configurations, stronger J produced a monotonic increase in peak nearest-neighbor concurrence, indicating faster correlation spread before local dissipation took over. Non-Markovian memory kernels and collective subradiant channels provided the strongest protection of coherence, with the memory kernel extending purity half-life most effectively and the collective bath raising late-time purity most strongly. By contrast, adding bonds or increasing N shortened half-life under local noise, consistent with an additive-channel effect. The combined bath gave the best overall balance between transient entanglement and the duration of the coherence window. A parallel classical Kuramoto comparator showed qualitatively similar coupling dependence, suggesting that many observed trends are not uniquely quantum but reflect a broader interaction-versus-noise competition.These results are strictly Level-A findings: numerical outcomes of the Lindblad equation applied to small toy chains with illustrative noise rates. Any mapping to microtubule lattices or to possible pharmacological levers, such as plasticity-driven connectivity changes or microtubule-stabilizing agents, remains hypothetical and is not validated by in vivo evidence. The pipeline is intended as a reproducible computational baseline for isolating mechanistic levers in open quantum networks.
The brain operates in a warm, noisy, aqueous environment that is generally expected to destroy fragile quantum superpositions almost instantly. Rather than debating whether stable macroscopic entanglement can survive in vivo, this Perspective asks a more focused question: can modest changes in nearest-neighbor coupling strength enhance the amplitude or duration of transient quantum correlations in microtubule-like lattices? We investigated this using deliberately minimal open quantum spin-chain models (XXZ and XY Hamiltonians on 4–12 sites) evolved under local amplitude damping and dephasing via the Lindblad master equation in QuTiP. Across linear chains, rings, ladders, and helical arrangements, increasing the coupling parameter J produced a clear monotonic rise in peak nearest-neighbor concurrence, while long-time purity remained essentially unchanged. A classical Kuramoto model of coupled noisy oscillators showed nearly identical scaling, indicating that the effect may reflect a general synchronization phenomenon. We place these results in the context of current quantum-biology literature and cautiously consider whether pharmacological agents capable of promoting cytoskeletal remodeling — such as the Cheung Glutamatergic Regimen — could, in principle, influence this coupling parameter. Although highly speculative, the work generates several concrete and testable experimental predictions.
Quantum approaches to consciousness remain controversial, partly because any putative quantum state in the brain is expected to decohere rapidly in a warm, hydrated, and noisy environment. The present manuscript does not attempt to solve that biological problem directly. Instead, it treats microtubule-related interpretation as a deliberately hypothetical analogy and asks a narrower Level-A question: under what generic open-system conditions can transient pairwise entanglement be enlarged in small noisy XXZ spin chains? In a minimal open XXZ spin-chain model evolved with the Lindblad master equation, stronger nearest-neighbor coupling consistently increased peak transient pairwise entanglement across several topologies and bath conditions. Among the tested environments, the memory-envelope condition gave the longest purity half-life, the collective condition increased late-time purity, and the combined bath is best described as a balanced compromise among selected diagnostics under the chosen parameters rather than as an optimized trade-off. The model is not a physical model of microtubules: it omits full 13-protofilament geometry, dynamic instability, microtubule-associated proteins, hydration structure, ionic screening, and realistic tubulin-scale calibration. On a strictly hypothetical Level-C reading, the two abstract model levers, stronger effective coupling and lower per-site dissipation, may be compared with broad classes of biological perturbation, such as glutamatergic plasticity and cytoskeletal stabilization, but not with named regimens or compounds as clinical routes to enhancement. No dosing schedule, clinical regimen, or cognitive-enhancement recommendation follows from the simulation. The proper experimental sequence is in vitro first, then animal work only if warranted, and human pilot work only after convergent preclinical support and safety review. Testable preclinical predictions include altered tryptophan-network fluorescence lifetimes, exciton migration signatures, superradiance-related optical behavior, and anesthetic sensitivity in controlled preparations. Negative in vitro optical or biophysical results would substantially weaken the biological relevance of the analogy. The manuscript should therefore be read as a reproducible toy-model study with a speculative microtubule analogy, not as evidence that pharmacological modulation can enhance cognition through quantum microtubule effects.
The pairwise entanglement of the Heisenberg XX chain with next-nearest-neighbor (NNN) interactions was investigated by using the concurrence measure. The results show that for the nearest-neighbor sites, the entanglement may be improved or suppressed depending on the magnitudes of the NNN coupling constant J, while for the next-nearest-neighbor sites, it always increases with the increase of |J|. The critical temperature Tc decreases with the increase of J for the nearest-neighbor entanglement and increases with the increase of |J| for the next-nearest-neighbor entanglement, respectively. We also show that the general Heisenberg XX model still can be used to create the entangled W states of three and four qubits, and that the presence of NNN coupling has no effect on the creation of four-qubit W states, while it shifts the instant of time at which the three-qubit W states are created.
Abstract The pairwise entanglement of the Heisenberg XX chain with next-nearest-neighbor (NNN) interac-tions was investigated by using the concurrence measure. The results show that for the nearest-neighbor sites,the entanglement may be improved or suppressed depending on the magnitudes of the NNN coupling constant J , while for the next-nearest-neighbor sites, it always increases with the increase of jJj . The critical tempera-ture T c decreases with the increase of J for the nearest-neighbor entanglement and increases with the increaseof jJj for the next-nearest-neighbor entanglement, respectively. We also show that the general Heisenberg XXmodel still can be used to create the entangled W states of three and four qubits, and that the presence ofNNN coupling has no efiect on the creation of four-qubit W states, while it shifts the instant of time at whichthe three-qubit W states are created.Key words Heisenberg XX chain, next-nearest-neighbor interaction, thermal entanglement 1 Introduction
The hard problem of consciousness, together with the expectation that quantum states should decohere rapidly in the warm and noisy brain, has long challenged quantum approaches to mind, including the orchestrated objective reduction framework. Even so, recent reports of room-temperature superradiance and long-range energy migration in tryptophan networks within microtubules have kept open the possibility that some quantum correlations might be transiently protected in biological settings. In a minimal open XXZ spin-chain model evolved with the Lindblad master equation, stronger nearest-neighbor coupling consistently increased peak transient pairwise entanglement across several topologies and bath conditions. Among the tested environments, the combined bath, which included non-Markovian memory and collective subradiant channels, produced the most favorable balance between entanglement amplitude and coherence lifetime. On a strictly hypothetical Level-C translational reading, these findings suggest two broad intervention levers: increasing effective coupling through cytoskeletal remodeling and reducing per-site dissipation through microtubule stabilization. Within that speculative frame, the Cheung Glutamatergic Regimen is considered as a possible route to the first lever, whereas low-dose lithium orotate and pulsed fisetin are considered as possible routes to the second. Three scheduling frameworks are outlined: daily combined maintenance, cyclic proliferation-consolidation, and baseline stabilization with as-needed plasticity boosts. Testable predictions include changes in gamma-band EEG during insight tasks, altered anesthetic emergence profiles, and shifts in microtubule optical behavior in vitro. This remains a thought experiment only and not medical advice. Any real-world investigation would require formal supervision and stringent safety monitoring because of known risks, including serotonin syndrome.Keywords: quantum biology, microtubule coherence, transient entanglement, glutamatergic plasticity, cognitive enhancement, open quantum systems