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arXiv · 2507.17910

Tensorial Spin-Phonon Relaxation Reveals Mode-Selective Relaxation Pathways in a Single-Molecule Magnet

Roman Dmitriev·Nosheen Younas·Yu Zhang·Andrei Piryatinski·Eric R. Bittner
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Abstract

Understanding and controlling spin relaxation in molecular qubits is essential for developing chemically tunable quantum information platforms. We present a fully first-principles framework for computing the spin relaxation tensor in a single-molecule magnet, \ce{VOPc(OH)8}, by combining density functional theory with a mode-resolved open-system formalism. By expanding the spin Hamiltonian in vibrational normal modes and evaluating both linear and quadratic spin-phonon coupling tensors via finite differences of the $g$-tensor, we construct a relaxation tensor that enters a Lindblad-type quantum master equation. Our formalism captures both direct (one-phonon) and resonant-Raman (two-phonon) relaxation processes. Numerical analysis reveals a highly mode-selective structure: only three vibrational modes dominate longitudinal ($T_1$) decoherence, while a single mode accounts for the majority of transverse ($T_2$) relaxation. The computed relaxation times show excellent agreement with experimental measurements, without any empirical fitting. These results demonstrate that first-principles spin-phonon tensors can provide predictive insight into decoherence pathways and guide the rational design of molecular qubits.

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Roman Dmitriev, Nosheen Younas, Yu Zhang, Andrei Piryatinski, Eric R. Bittner. 2025-07-23. Tensorial Spin-Phonon Relaxation Reveals Mode-Selective Relaxation Pathways in a Single-Molecule Magnet. https://arxiv.org/abs/2507.17910

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