Large nuclear spin polarization in gate-defined quantum dots using a single-domain nanomagnet

TL;DR

This paper demonstrates a method to achieve high nuclear spin polarization (~50%) in gate-defined quantum dots by using a single-domain nanomagnet, which modifies nuclear spin dynamics and reduces decoherence.

Contribution

It introduces a novel approach employing a nanomagnet to control nuclear spin polarization in quantum dots, surpassing previous polarization levels.

Findings

Achieved ~50% nuclear spin polarization in lateral quantum dots.

Modified nuclear spin dynamics via an inhomogeneous magnetic field.

Developed a rate equation model to explain the polarization process.

Abstract

The electron-nuclei (hyperfine) interaction is central to spin qubits in solid state systems. It can be a severe decoherence source but also allows dynamic access to the nuclear spin states. We study a double quantum dot exposed to an on-chip single-domain nanomagnet and show that its inhomogeneous magnetic field crucially modifies the complex nuclear spin dynamics such that the Overhauser field tends to compensate external magnetic fields. This turns out to be beneficial for polarizing the nuclear spin ensemble. We reach a nuclear spin polarization of ~50%, unrivaled in lateral dots, and explain our manipulation technique using a comprehensive rate equation model.