High-fidelity EDSR in Si/SiGe Wiggle Wells

Si/SiGe quantum wells that incorporate Ge concentration oscillations, known as long-period Wiggle Wells, have been shown to enhance the Dresselhaus spin-orbit coupling of conduction-band electrons. Such intrinsic spin-orbit coupling is desirable when performing spin-qubit gate operations based on electric dipole spin resonance (EDSR) because it eliminates the need for external micromagnets. However, random-alloy disorder plays a key role in this materials system by spatially randomizing the valley splitting and the valley phase φ_s,s, and it has not been fully accounted for in recent EDSR analyses. Here, we show that alloy disorder affects EDSR in two main ways. First, the Rabi frequency Ω acquires a dependence on the valley phase, given by cosφ_s,s, which causes spatial randomization of Ω. Despite this variability, we show that fast EDSR can be achieved at most locations across a given sample. Second, a new Rabi driving mechanism emerges, enabled by valley dipoles and the hybridization of ground and excited valley states, which arise from alloy disorder and EDSR driving, respectively. This mechanism is dominant in regions of low valley splitting. Alloy disorder can therefore strengthen EDSR, but it can also cause gradients in Ω that lead to dephasing in the rotating frame. We explore this problem by first locating "sweet spots," where EDSR is relatively insensitive to electric-field fluctuations. We then show that high-fidelity Rabi oscillations can be achieved in the presence of realistic charge noise. These results suggest that Wiggle Wells are a promising platform for high-quality, micromagnet-free gate operations.