Optimisation of electron spin qubits in electrically driven multi-donor quantum dots

Multi-donor quantum dots have been at the forefront of recent progress in Si-based quantum computation. Among them, 2P:1P spin qubits have a built-in dipole moment, making them ideal for electron dipole spin resonance (EDSR) using the donor hyperfine interaction. The development of such all-electrical spin qubits requires a full understanding of their EDSR and coherence properties, in which multi-donor dot qubits are expensive to model computationally due to the multi-valley nature of their ground state. Here we examine the impact of qubit geometry and nearby charge defects on the electrical operation and coherence of a 2P:1P electron spin qubit. We report fast EDSR, with T_π ∼ 10 - 50 nanoseconds and a Rabi ratio (T₁/T_π) ∼ 10⁶. The fastest EDSR time T_π occurs when the 2P:1P axis is ? [111], while the best Rabi ratio occurs when it is ? [100]. Sensitivity to random telegraph noise due to nearby charge defects depends strongly on the location of the nearby defects with respect to the qubit. The qubit is robust against 1/f noise provided it is operated away from the charge anti-crossing. Entanglement via exchange is several orders of magnitude faster than dipole-dipole coupling. These findings pave the way towards fast, low-power, coherent and scalable donor dot-based quantum computing.