The Biological Qubit: Calcium Phosphate Dimers, Not Trimers

S Agarwal and DR Kattnig and CD Aiello and AS Banerjee, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 14, 2518-2525 (2023).

DOI: 10.1021/acs.jpclett.2c03945

The Posner molecule (calcium phosphate trimer, Ca9(PO4)6) has been hypothesized to function as a biological quantum information processor due to its supposedly long-lived entangled 31P nuclear spin states. This hypothesis was challenged by our recent finding that the molecule lacks a well-defined rotational axis of symmetry-an essential assumption in the proposal for Posner-mediated neural processing-and exists as an asymmetric dynamical ensemble. Following up, we investigate here the spin dynamics of the molecule's entangled P-31 nuclear spins within the asymmetric ensemble. Our simulations show that entanglement between two nuclear spins prepared in a Bell state in separate Posner molecules decays on a subsecond time scale-much faster than previously hypothesized, and not long enough for supercellular neuronal processing. Calcium phosphate dimers (Ca-6(PO4)(4)) however, are found to be surprisingly resilient to decoherence and are able to preserve entangled nuclear spins for hundreds of seconds, suggesting that neural processing might occur through them instead.

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