Simulation and measurement of stray fields for the manipulation of spin-qubits in one- and two-dimensional arrays

TL;DR

This study combines simulations and microscopy to analyze how polycrystallinity and material choice in micromagnets affect stray fields, impacting the control and scalability of spin-qubit arrays.

Contribution

It reveals the influence of polycrystalline structure and material properties on stray fields, guiding better design of micromagnets for spin-qubit manipulation.

Findings

Polycrystallinity in Co magnets causes up to 0.5 GHz qubit frequency shifts.

Fe magnets produce higher field gradients (>1 mT/nm) and are advantageous over Co.

Designed a 2D nanomagnet array for spin qubit control.

Abstract

The inhomogeneous magnetic stray field of micromagnets has been extensively used to manipulate electron spin qubits. By means of micromagnetic simulations and scanning superconducting quantum interference device microscopy, we show that the polycrystallinity of the magnet and non-uniform magnetization significantly impact the stray field and corresponding qubit properties. We find that the random orientation of the crystal axis in polycrystalline Co magnets alters the qubit frequencies by up to 0.5 GHz, compromising single qubit addressability and single gate fidelities. We map the stray field of Fe micromagnets with an applied magnetic field of up to 500 mT (mimicking conditions when operating qubits), finding field gradients above 1 mT/nm. The measured gradients and the lower magnetocrystalline anisotropy of Fe demonstrate the advantage of using Fe instead of Co for magnets in spin qubit devices. These properties of Fe also enabled us to design a 2D arrangement of nanomagnets for driving spin qubits distributed on a 2D lattice.