Magnetic gradient free two axis control of a valley spin qubit in SiGe

TL;DR

This paper demonstrates a novel method for two-axis control of a valley spin qubit in SiGe quantum dots, utilizing valley states as an effective magnetic field gradient without external magnetic field gradients.

Contribution

The work introduces a valley-based approach for qubit control in SiGe, eliminating the need for magnetic field gradients and simplifying quantum dot scalability.

Findings

Valley states enable two-axis qubit control without magnetic field gradients.

The valley-induced g-factor difference is universal and electrically tunable.

Qubit rotation rate increases linearly with external magnetic field.

Abstract

Spins in SiGe quantum dots are promising candidates for quantum bits but are also challenging due to the valley degeneracy which could potentially cause spin decoherence and weak spin-orbital coupling. In this work we demonstrate that valley states can serve as an asset that enables two-axis control of a singlet-triplet qubit formed in a double quantum dot without the application of a magnetic field gradient. We measure the valley spectrum in each dot using magnetic field spectroscopy of Zeeman split triplet states. The interdot transition between ground states requires an electron to flip between valleys, which in turn provides a g-factor difference $\Delta g$ between two dots. This $\Delta g$ serves as an effective magnetic field gradient and allows for qubit rotations with a rate that increases linearly with an external magnetic field. We measured several interdot transitions and found that this valley introduced $\Delta g$ is universal and electrically tunable. This could potentially simplify scaling up quantum information processing in the SiGe platform by removing the requirement for magnetic field gradients which are difficult to engineer.