Electrical control of drifting spin coherence in GaAs quantum well

Y. Matsumoto, X.-F. Liu, Arne Ludwig +5 more

Abstract Fast electrical spin rotations in quantum dots require strong spin-charge hybridization, but the same hybridization can increase sensitivity to detuning noise. In a double-quantum-dot (DQD) flopping-mode qubit, the sweet-spot width and the Rabi enhancement are both tied to the same orbital splitting, limiting post-fabrication optimization of the speed-coherence trade-off. Here, we demonstrate a GaAs triple-quantum-dot (TQD) flopping-mode qubit in which the detuning of the third dot, ϵ 34 , provides an additional electrical tuning parameter for orbital-band flattening. Tuning ϵ 34 flattens the qubit-frequency dependence on the detuning of the target DQD while maintaining strong spin-charge hybridization, enabling electrically driven Rabi frequencies above 100 MHz. We then use feedforward-neural-network (FNN) feedback to track slow qubit-frequency drift and connect this engineered operating point to high-fidelity gates. This feedback suppresses slow qubit-frequency fluctuations, reducing their standard deviation to 388 kHz, and yields a π /2 gate fidelity of 99.56% with a 4.05 ns gate time. These results identify TQD orbital-band engineering as an electrical route for tuning the speed-coherence trade-off, complementary to material-intrinsic spin-orbit coupling and fixed micromagnet geometry.

Rudolf Bratschitsch, Zhigang Chen, Steven T. Cundiff +1 more

Y. Ohno, R. Terauchi, T Adachi +2 more

Jared K. Wahlstrand, Haipeng Zhang, John E. Sipe +1 more

A static electric field enables 1 + 2-photon coherent control of the photoexcited carrier population in semiconductors. A theory based on the Franz-Keldysh effect is compared to results of an experiment in (100) GaAs.

M. V. Gurudev Dutt, Jun Cheng, Yanwen Wu +7 more

Impulsive stimulated Raman excitation with coherent optical fields is used for controlling the electron spin coherence in a charged $\mathrm{GaAs}$ quantum dot ensemble through an intermediate charged exciton (trion) state. The interference between two stimulated Raman two-photon quantum mechanical pathways leading to the spin coherence allows us to control the electron spin coherence on the time scale of the Larmor precession frequency. We also demonstrate, both theoretically and experimentally, that ultrafast manipulation of the spin coherence is possible on the time scale of the optical laser frequency, and analyze the limitations due to the trion and spin decoherence times.

Timothy M. Sweeney