Decoherence

Decoherence is the disruption of quantum superposition due to energy or information interaction with the classical environment. Consequently, quantum technology is generally developed in ultracold isolation, and physicists are skeptical of quantum computing in the "warm, wet and noisy" brain.

However, biological systems may delay decoherence in several ways [36]. One is to isolate the quantum system from environmental interactions by screening/shielding. Intraprotein hydrophobic pockets are screened from external van der Waals thermal interactions; MTs may also be shielded by counterion Debye plasma layers (due to charged C-termini tails on tubulin) and by water-ordering actin gels [95]. Biological systems may also exploit thermodynamic gradients to give extremely low effective temperatures [152].

Another possibility concerns decoherence-free subspaces. Paradoxically, when a system couples strongly to its environment through certain degrees of freedom, it can effectively "freeze" other degrees of freedom (by a sort of quantum Zeno effect), enabling coherent superpositions and entanglement to persist [163]. Metabolic energy supplied to MT collective dynamics (e. g. Fröhlich coherence) can counter decoherence (in the same way that lasers avoid de-coherence at room temperature). Finally, MT structure seems ideally suited for topological quantum error correction by the Aharonov-Bohm effect [95].

Attempting to disprove the relevance of quantum states in consciousness, Max Tegmark ([228], cf. [203]) calculated MT decoherence times of 10~13s, far too brief for neural activities. However, Tegmark did not address Orch OR nor any previous proposal, but his own quantum MT model, which he did indeed successfully disprove. Hagan et al. [85] recalculated MT decoherence times with Tegmark's formula43 but based on stipulations of the Orch OR model. For example, Tegmark used superposition of solitons "separated from

The time tau to decoherence due to the long-range electromagnetic influence of an environmental ion is t ~ 4ne"nq2smkt where T is the temperature, m is the mass of the ionic species, a is the distance from the ion to the position of the superposed state, N is the number of elementary charges comprising that superposed state, and s is the maximal separation between the positions of the tubulin mass in the alternative geometries of the quantum superposition.

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