Electric-Field Programmable Rashba Qubits: Cross-Material Operating Windows for Frequency Allocation and Leakage Control

This work presents a cross-material, design-oriented framework for electrically tunable spin–orbit qubits, focusing on realistic operating windows for four key semiconductor platforms: GaAs, InAs, InSb, and SiGe. Building on validated two-band models, we introduce a unified set of energy-based figures of merit— qubit gap ($\Delta_q$), isolation energy ($\Delta_{iso}$), and anharmonicity ($A$)—to assess qubit performance and leakage suppression within experimentally achievable magnetic fields (GaAs/SiGe below 2~T; InAs/InSb up to 5~T). The framework reveals explicit trade-offs between controllability and fidelity by mapping the combined effects of Rashba ($\alpha$) and Dresselhaus ($\beta$) spin–orbit couplings, vertical electric field $F$, and valley splitting parameters ($\Delta_v$, $t_v$). Results highlight that InAs offers strong intrinsic tunability with minimal leakage, while GaAs requires careful co-tuning of $\alpha$ and $\beta$, and SiGe performance depends critically on maximizing $\Delta_v$ and minimizing $t_v$. These findings provide practical guidelines for material selection and device optimization, bridging theoretical modeling with experimental implementation for next-generation semiconductor qubits.