Modular nanomagnet design for spin qubits confined in a linear chain

TL;DR

This paper introduces a modular nanomagnet design for linear chain spin qubits, enabling scalable, addressable quantum gates with strong driving fields and minimal crosstalk, validated through simulations and microscopy.

Contribution

The paper presents a novel nanomagnet configuration for linear spin qubit chains that enhances addressability and scalability in quantum computing architectures.

Findings

Design achieves strong driving fields with weak dephasing gradients

Micromagnetic simulations confirm effective qubit control

Fabrication and microscopy validate the nanomagnet design

Abstract

On-chip micromagnets enable electrically controlled quantum gates on electron spin qubits. Extending the concept to a large number of qubits is challenging in terms of providing large enough driving gradients and individual addressability. Here we present a design aimed at driving spin qubits arranged in a linear chain and strongly confined in directions lateral to the chain. Nanomagnets are placed laterally to one side of the qubit chain, one nanomagnet per two qubits. The individual magnets are "U"-shaped, such that the magnetic shape anisotropy orients the magnetization alternately towards and against the qubit chain even if an external magnetic field is applied along the qubit chain. The longitudinal and transversal stray field components serve as addressability and driving fields. Using micromagnetic simulations we calculate driving and dephasing rates and the corresponding qubit quality factor. The concept is validated with spin-polarized scanning electron microscopy of Fe nanomagnets fabricated on silicon substrates, finding excellent agreement with micromagnetic simulations. Several features required for a scalable spin qubit design are met in our approach: strong driving and weak dephasing gradients, reduced crosstalk and operation at low external magnetic field.