Kinetic Cluster Embedding for Qubit Decoherence in Dissipative Spin Baths

arXiv:2611.08830v1 Announce Type: new Abstract: Interpreting the decoherence of a spin qubit requires knowing how the surrounding bath spins behave: whether they fluctuate independently, exchange polarization incoherently, or evolve as coherent groups. These processes can yield the same Hahn-echo coherence time yet produce different coherence signals under pulse control of the qubit. Existing theoretical approaches either capture bath correlations at a cost that grows combinatorially with spin-bath cluster size or neglect polarization transport altogether. We introduce kinetic cluster embedding (KCE), which uses a single dimensionless parameter, comparing the flip-flop coupling of a spin pair with its detuning and linewidth, to decide how each pair must be treated.