On the Potential of Microtubules for Scalable Quantum Computation

TL;DR

This work advances a QED cavity view of microtubules in which tubulin dipoles strongly couple to ordered-water dipole quanta, extending coherence to timescales near $t_{\rm decoh} \sim \mathcal{O}(10^{-6})$ s under physiological conditions. It links soliton dynamics in a nonlinear sigma-model description to quantum coherent states, proposing that double helices of snoidal waves enable dissipationless transport and that MT networks can realize high-dimensional quDits organized in hexagonal unit cells, with MAPs functioning as logical interconnects. The authors outline a scalable biocomputation framework where quDits are entangled within decoherence windows and manipulated by dipole-dipole interactions and external fields, supported by a detailed Rabi-splitting experimental roadmap. They propose experimental verifications using Rabi-splitting and SPR-based photonic probes to test MTs as viable biomolecular quantum substrates, and discuss the potential to realize ambient-temperature quantum information processing in living systems or engineered MT networks. If validated, this line of research could redefine biological information processing and inspire MT-inspired quantum devices operating in wet environments.

Abstract

We examine the quantum coherence properties of tubulin heterodimers arranged into the protofilaments of cytoskeletal microtubules. In the physical model proposed by the authors, the microtubule interiors are treated as high-Q quantum electrodynamics (QED) cavities that can support decoherence-resistant entangled states under physiological conditions, with decoherence times of the order of $\mathcal{O}(10^{-6})$ sec. We identify strong electric dipole interactions between tubulin dimers and ordered water dipole quanta within the microtuble interior as the mechanism responsible for the extended coherence times. Classical nonlinear (pseudospin) $σ$-models describing solitonic excitations are reinterpreted as emergent quantum-coherent-or possibly pointer-states, arising from incomplete collapse of dipole-aligned quantum states. These solitons mediate dissipation-free energy transfer along microtubule filaments. We discuss logic-gate-like behavior facilitated by microtubule-associated proteins, and outline how such structures may enable scalable, ambient-temperature quantum computation, with the fundamental unit of information storage realized as a quDit encoded in the tubulin dipole state. We further describe a process akin to decision making that emerges following an external stimulus, whereby optimal, energy-loss-free signal and information transport pathways are selected across the microtubular network. Finally, we propose experimental approaches-including Rabi-splitting spectroscopy and entangled surface plasmon probes-to validate the use of biomatter as a substrate for scalable quantum computation.

Figures (12)

• Figure 1: A typical potential, with two degenerate non-trivial minima at $\phi=\pm \, C$, for a soliton solution in a (1+1)-dimensional real-scalar $\phi$ field theory.
• Figure 2: The profile of a typical one-dimensional static kink soliton \ref{['kink']} (pictured here for indicative values $m=\sqrt{\lambda}=1$, and $x_0=1$). The same profile characterizes the traveling kink wave \ref{['boostedkink']}, obtained upon the replacement of $x-x_0$ in \ref{['kink']} by the Lorentz boosted coordinate $\gamma \, (x-x_0 - vt)$, $\gamma = \frac{1}{\sqrt{1-v^2}}$, where $v>0 \, (<0)$ corresponds to left (right) movers.
• Figure 3: Left : A microtubule (MT) (a), showing individual dimer subunits and their dimensions (b) (1 Angstrom = 0.1 nm). The walls consist of tubulin protein dimers ((c) GTP tubulin, (d) GDP tubulin), which are arranged usually in 12 or 13 helical protofilaments (vertical chain-like structures, parallel to the long axis of MT). The interior (e) is full of ordered water molecules. In the cavity model of MT!mn1mmn1, a thin interior layer near the dimer walls (f) behaves as a high-Q electromagnetic cavity. Right Picture: A network of microtubules typical of the neuronal cytoskeleton. The "rungs" cross-connecting MTs are microtubule associated proteins (MAP MershinFlies2004) (figures from ref. mmn1)
• Figure 4: The structure of the cytoskeleton microtubule (MT). The arrows indicate the orientation of the permanent dipole moments of the tubulin heterodimers with respect to the MT surface. The permanent dipole moments of the tubulin dimers are all oriented in such a way that the spherical polar angle of the dipole vectors with respect to the symmetry axis of the MT (assumed here along the $z$ direction) is approximately TBCC$\Theta_0 \simeq 29^{\,\rm o}$. Picture from ref. mexico.
• Figure 5: Tubulin neighborhood in the hexagonal unit cell of the microtubule. The distance between dimers is $d$. The heterodimer helix direction is defined by the height, $h$. The typical values of parameters are: $a=8\, \rm nm$, $b=5.87\, \rm nm$, $c=7.02\,\rm nm$, $d = 5\, \rm nm$, $h = 4.9\, \rm nm$, $\theta_1 =0$, $\theta_2 =58.2^{\,\rm o}$, $\theta_3 = 45.58^{\,\rm o}$Sl2TBCCTHSTGTJT. This structure will play the rôle of the quDit basic information storage unit in our modelling of the MT as a biocomputer.