Vacancy aggregation enhances NV- spin coherence in diamond: a cluster-correlation-expansion study of multi-vacancy spin baths in semiconductors

arXiv:2609.24295 (cond-mat)

Abstract:Annealing a semiconductor makes its vacancies mobile; they aggregate into multi-vacancy complexes that often carry spin. Such centres are a magnetic-noise source for any spin qubit among them, in silicon and silicon carbide as well as in diamond, and they are accordingly blamed for NV- decoherence in irradiated and implanted diamond, with two coherence records credited to removing them. Cluster-correlation-expansion simulations driven by published electron-paramagnetic-resonance parameters invert that attribution. At a fixed paramagnetic spin density a multi-vacancy bath gives a Hahn-echo coherence time 2.7-4.4 times longer than a bath of isolated negative vacancies, constant over three decades of concentration. A bath dephases the qubit because its spins exchange spin projections with one another, and two can exchange only if their transition frequencies match. A fine-structure splitting shifts those frequencies. Were every defect on the same crystallographic site, all would shift alike and still match: worth only a factor 1.3. Real defects occupy symmetry-equivalent sites pointing in different directions, so neighbours land at different frequencies and stop exchanging: a further 1.9. What governs the coherence time is therefore the fraction of bath pairs sharing a transition frequency, not the zero-field splitting. Vacancy aggregation extends NV- spin coherence rather than shortening it.

Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)

arXiv:2609.24295 [cond-mat.mtrl-sci]

(or arXiv:2609.24295v1 [cond-mat.mtrl-sci] for this version)

https://doi.org/10.48550/arXiv.2609.24295 arXiv-issued DOI via DataCite (pending registration)

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