## Quantum information in neural systems

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- Category: News
- Published on Wednesday, 13 October 2021 11:29
- Written by Danko Georgiev
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We exist in the universe and, consequently, obey its physical laws whatever those physical laws may be. Classical physics, however, describes a deterministic clockwork world that is unable to accommodate causally effective conscious experiences. This leads to insurmountable problems with the theory of evolution, including a lack of explanation of how consciousness could be tolerated by natural selection. Fortunately, quantum mechanics supports a radically different picture of the physical world in which the fabric of reality is comprised of quantum probability amplitudes for potential physical events, whose actual occurrence is decided indeterministically by the inherent propensity of quantum systems to produce a definite physical outcome upon measurement. This provides a fertile ground for the physical modeling of consciousness due to dichotomy between what exists in the form of quantum states, and what can be observed in the form of quantum observables.

In our new article published in *Symmetry*, we utilize the Schrödinger equation, together with the Planck–Einstein relation between energy and frequency, in order to determine the appropriate quantum dynamical timescale of conscious processes. Furthermore, with the help of a simple two-qubit toy model we illustrate the importance of non-zero interaction Hamiltonian for the generation of quantum entanglement and manifestation of observable correlations between different measurement outcomes. Employing a quantitative measure of entanglement based on Schmidt decomposition, we show that quantum evolution governed only by internal Hamiltonians for the individual quantum subsystems preserves quantum coherence of separable initial quantum states, but eliminates the possibility of any interaction and quantum entanglement. The presence of non-zero interaction Hamiltonian, however, allows for decoherence of the individual quantum subsystems along with their mutual interaction and quantum entanglement. The presented results show that quantum coherence of individual subsystems cannot be used for cognitive binding because it is a physical mechanism that leads to separability and non-interaction. In contrast, quantum interactions with their associated decoherence of individual subsystems are instrumental for dynamical changes in the quantum entanglement of the composite quantum state vector and manifested correlations of different observable outcomes. Thus, fast decoherence timescales could assist cognitive binding through quantum entanglement across extensive neural networks in the brain cortex.