Micromagnet-free operation of electron spin qubits in Si/Si$_{1-x}$Ge$_x$ vertical double quantum dots

TL;DR

This paper demonstrates a micromagnet-free method for fast, electrically controlled electron spin qubits in Si/SiGe double quantum dots, leveraging spin-orbit interaction and valley splitting for scalable quantum computing.

Contribution

It introduces a vertical Si/SiGe double quantum dot architecture enabling full electrical control of spin qubits without micromagnets, enhancing scalability.

Findings

Large valley splitting (~250 μeV) observed.

Ultrafast single qubit gates (<1 ns) achieved.

Electrical control via EDSR and ESR demonstrated.

Abstract

We study a vertical double quantum dot (DQD) in a Si/Si$_{1-x}$Ge$_x$/Si double-well heterostructure for full electrical control of electron Loss-DiVincenzo (LD) spin qubits, using realistic device modeling and numerical simulations. Due to the emerging spin-orbit interaction in the DQD, as well as strain from the gate electrodes, small (percentage range) but finite $g$ tensor variations emerge. In addition, we find a large valley splitting, on the order of $E_v{\sim}250\,\mu$eV. As a result, multiple avenues for fast electrical single qubit rotations emerge. An ac electric field gives rise to electric dipole spin resonance (EDSR), while electron spin resonance (ESR) in the presence of an ac magnetic field can be electrically controlled by local gates due to varying $g$ factors in DQDs. We also show that shuttling between neighboring dots, in vertical and horizontal direction, results in ultrafast single qubit gates of less than a nanosecond. Remarkably, this DQD architecture completely eliminates the need for micromagnets, significantly facilitating the scalability of LD spin qubits in semiconductor foundries.