2025/07/23 by Dmitriev, Roman, Younas, Nosheen, Zhang, Yu +2 · 1 citation
#FOS: Physical sciences #Quantum Physics (quant-ph)
paper · doi:10.48550/arxiv.2507.17910
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, \ceVOPc(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 (T1) decoherence, while a single mode accounts for the majority of transverse (T2) 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.