Yuta Matsumoto

Electron spins in semiconductor quantum dots (QD) hold promise for hardware innovation towards quantum computers and quantum simulators. In order to realize reliable quantum hardware, the single-spin manipulation speed (Rabi frequency) must be sufficiently faster than the coherence time. While Si QD devices realize high-fidelity qubits by elongating coherence times with their nuclear-spin-free environment, GaAs QDs succeed in quantum simulation with   their flexible control and Ge QDs provide fast spin manipulation with strong spin orbit interaction. A general method to achieve long coherence time and fast spin manipulation speed, which is independent of host materials, is strongly desired in the future to variously apply quantum technologies.

In this work, we achieve both fast spin manipulation speed and long coherence in a multiple GaAs QD device. The Rabi frequency is increased to several hundred MHz using a micromagnet design optimized for the inter-dot spin shuttling among three QDs. We also achieve a coherence time (T2*) of up to 1us using feedback control on the control microwave to suppress the difference from the qubit frequency. The control fidelity of the improved single-spin-qubit system will be discussed. Since our method relies only on device designing and software implementation, it is applicable to any QD device, regardless of the material choice. We believe that this work would be an important block in future quantum hardware.