Modular nanomagnet design for spin qubits confined in a linear chain

Abstract

On-chip micromagnets enable electrically controlled quantum gates on electron spin qubits. Extending the concept to many qubits is challenging in terms of providing large enough driving gradients and individual addressability. Here we present a design aimed to drive spin qubits arranged in a linear chain with strong lateral confinement, such as in a silicon finFET or nanowire architecture. ‘U’-shaped nanomagnets are placed laterally to one side of the qubit chain. The magnetic shape anisotropy orients the magnetization in the arms of the ‘U’s alternately towards and against the qubit chain. Using micromagnetic simulations we optimize driving and dephasing gradients with respect to the qubit quality factor. Iron nanomagnets fabricated on silicon substrates are investigated by spin-polarized scanning electron microscopy, finding excellent agreement with our micromagnetic simulations. This scalable design for spin qubits provides strong driving gradients (3 mT/nm), low dephasing and reduced crosstalk with Larmor frequency difference > 2 GHz between neighboring qubits.