The Posner molecule: Ab initio investigations of a potential biomolecular qubit

The Posner molecule, Ca₉(PO₄)₆, is of central biochemical relevance. It has also gained recent attention for its hypothesized role as a biological quantum information processor. The molecule is thought to maintain long-lived nuclear spin coherences and entanglement among its ³¹P nuclei, which could potentially be used for liquid-state nuclear magnetic resonance quantum computing.

Central to the alleged favorable quantum characteristics of the molecule is the purported symmetrical arrangement of its ³¹P nuclei. An S₆ symmetry, that has been widely assumed, renders the six nuclei magnetically equivalent and simplifies the spin coupling network. In contrast, a lower point-group symmetry is likely to adversely affect the ability of the system to sustain long-lived spin coherences.

Using extensive ab initio molecular dynamics and structural relaxation calculations on over 10,000 molecular geometries, we establish that the Posner molecule predominantly assumes low symmetry structures (C_s and C_i) at room temperature, instead of higher symmetry configurations explored previously. We describe how this critical finding may affect the molecule's viability as a biomolecular qubit.