Abstract
The coherence of electron spin qubits in semiconductor quantum dots suffers mostly from low-frequency noise. During the last 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 high-frequency charge noise rather than the quasi-static noise inherent to any semiconductor device. We employed a feedback control technique to actively suppress the latter, demonstrating a $\pi$-flip gate fidelity as high as $99.04\pm 0.23\,\%$ 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.
Highlights
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
While the spin coherence is dominated by lowfrequency noise, the control fidelity of a qubit is often impeded by noise at higher frequencies [11,12,13,14]
The single-electron spin qubit reported in this work is located in the middle quantum dot (QD) and manipulated by the electric-dipole spin resonance (EDSR) [19,20,21]
Summary
Since electrical manipulation of a single spin was demonstrated in semiconductor quantum dots [1], enormous efforts have been devoted to improve spin coherence by controlling [2,3] or eliminating [4,5,6] nuclear spins, a. The underlying relationship between the control fidelity and spin coherence remains elusive, because there are different noise sources that could dominate in different frequency ranges, such as nuclear spin diffusion and charge fluctuators (see Fig. 1). The former shows a 1=fβ spectrum with 3 > β > 1 in GaAs [15,16] and possibly in natural Si devices [17], while the latter with β ∼ 1 can dominate in 28Si devices [6]. We analyze how the low-frequency and high-frequency parts of the noise compete with each other and discuss the limitations of the high-fidelity control
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