Electric-field control and noise protection of the flopping-mode spin qubit

We propose and analyze a "flopping-mode" mechanism for electric dipole spin resonance based on the delocalization of a single electron across a double quantum dot confinement potential. Delocalization of the charge maximizes the electronic dipole moment compared to the conventional single-dot spin resonance configuration. We present a theoretical investigation of the flopping-mode spin qubit properties through the crossover from the double-to the single-dot configuration by calculating effective spin Rabi frequencies and single-qubit gate fidelities. The flopping-mode regime optimizes the artificial spin-orbit effect generated by an external micromagnet and draws on the existence of an externally controllable sweet spot, where the coupling of the qubit to charge noise is highly suppressed. We further analyze the sweet spot behavior in the presence of a longitudinal magnetic field gradient, which gives rise to a second-order sweet spot with reduced sensitivity to charge fluctuations.