Coherence of a Driven Electron Spin Qubit Actively Decoupled from Quasistatic Noise

The coherence of electron spin qubits in semiconductor quantum dots suffers mostly from low-frequency noise.During the past decade, efforts have been devoted to mitigate such noise by material engineering, leading to substantial enhancement of the spin dephasing time for an idling qubit.However, the role of the environmental noise during spin manipulation, which determines the control fidelity, is less understood.We demonstrate an electron spin qubit whose coherence in the driven evolution is limited by highfrequency charge noise rather than the quasistatic noise inherent to any semiconductor device.We employ a feedback-control technique to actively suppress the latter, demonstrating a π-flip gate fidelity as high as 99.04 Æ 0.23% in a gallium arsenide quantum dot.We show that the driven-evolution coherence is limited by the longitudinal noise at the Rabi frequency, whose spectrum resembles the 1=f noise observed in isotopically purified silicon qubits.