Measuring high field gradients of cobalt nanomagnets in a spin-mechanical setup

TL;DR

This paper reports the fabrication and characterization of cobalt nanomagnets with high magnetic field gradients for spin-mechanical quantum systems, demonstrating preserved spin coherence and measurable spin-mechanics coupling.

Contribution

It introduces a cobalt nanomagnet fabrication method with focused electron beam-induced deposition and characterizes its magnetic properties for quantum hybrid systems.

Findings

Maximum magnetic field gradient of 170 kT/m measured

Spin coherence maintained at 20 μs up to 25 kT/m

Observation of spin-mechanics coupling effects

Abstract

Hybrid systems composed of a single nitrogen-vacancy center spin magnetically coupled to a macroscopic mechanical resonator constitute promising platforms for the realization of quantum information protocols and for quantum sensing applications. The magnetic structure that mediates the interaction must ensure high field gradients while preserving the spin and mechanical properties. We present a spin-mechanical setup built around a cobalt nanomagnet grown with focused electron beam-induced deposition. The magnetic structure is fully characterized, and a maximum gradient of $170\,\mathrm{kT/m}$ is directly measured at a spin-oscillator distance of a few hundred nanometers. Spin coherence was preserved at the value of $20\,\mathrm{ \mu s}$ up to a gradient of $25\,\mathrm{kT/m}$. The effect of the mechanical motion onto the spin dynamics was observed, thus signifying the presence of spin-mechanics coupling. Given the noninvasive nature of the nanomagnet deposition process, we foresee the adoption of such structures in hybrid platforms with high-quality factor resonators, in the "magnet on oscillator" configuration.