Design and Optimization of Spin Dynamics in Ge Quantum Dots: g-Factor Modulation, Geometry-Induced Dephasing Sweet Spots, and Phonon-Induced Relaxation

Abstract:Gate geometry and bias asymmetry can be used to engineer spin dynamics in gate-defined Ge hole quantum dots by reshaping the confinement potential and driving transitions between distinct confinement regimes. In this work, we show that these transitions strongly modify wavefunction localization, heavy-hole/light-hole mixing, and the effective vertical electric field, leading to pronounced g-factor modulation and geometry-induced dephasing sweet spots where the qubit becomes first-order insensitive to vertical electric-field fluctuations. We further find that phonon-induced spin relaxation exhibits a strong dependence on device size and bias, with T1 following a magnetic-field scaling close to B-9, consistent with Rashba-dominated heavy-hole spin dynamics. These results are obtained using a comprehensive three-dimensional simulation framework for strained Si0.2Ge0.8/Ge gate-defined hole spin qubits, combining realistic electrostatics with a four-band Luttinger-Kohn Hamiltonian. Unlike simplified symmetric confinement models, this approach captures asymmetric wavefunction redistribution, g-tensor anisotropy, and the coupled electrostatic and spin response of realistic devices. Our results establish gate pattern and bias design as practical tools for optimizing spin coherence in Ge hole-spin qubits.

Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

arXiv:2509.10731 [cond-mat.mes-hall]

(or arXiv:2509.10731v4 [cond-mat.mes-hall] for this version)

https://doi.org/10.48550/arXiv.2509.10731 Focus to learn more arXiv-issued DOI via DataCite

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