Phonon-coupled hole-spin qubits in high-purity germanium: design and modeling of a scalable architecture

Abstract

We present a design and modeling of a scalable quantum processor architecture utilizing hole-spin qubits defined in gate-controlled germanium (Ge) quantum dots, where coherent spin–phonon coupling is predicted to facilitate qubit manipulation and long-range interactions. The architecture exploits the strong, electrically tunable spin–orbit interactions intrinsic to hole states in Ge, integrated with high-quality phononic crystal cavities to enable fully electrical qubit control and phonon–mediated coupling. Employing a streamlined simulation framework built upon multiband k⋅p modeling and finite-element methods, we quantify key performance metrics, including electrically tunable g-factors ranging from 1.3 to 2.0, spin–phonon coupling strengths up to 6.3MHz, phononic cavity quality factors exceeding 104, and phonon–mediated spin relaxation times (T1) reaching milliseconds. The proposed architecture concurrently achieves extended spin coherence and rapid gate operations through strategic electric field modulation and engineered phononic bandgap environments. Furthermore, isotopically enriched, high-purity Ge crystals significantly enhance device coherence by minimizing disorder and hyperfine interactions. This integrated approach, merging advanced materials engineering, precise spin–orbit coupling, and phononic cavity design, establishes a promising complementary metal–oxide–semiconductor-compatible pathway toward scalable, high-fidelity quantum computing.