Hybrid setup for stable magnetic fields enabling robust quantum control

TL;DR

This paper presents a cost-effective hybrid magnetic field setup combining rare-earth magnets and coils, achieving high stability and tuneability, enabling long coherence times and sensitive magnetic field measurements for quantum applications.

Contribution

The authors introduce a novel hybrid magnetic field assembly with enhanced stability and tuneability, suitable for compact quantum devices and precision sensing.

Findings

Achieved magnetic field strength of ~10.9 mT with less than 10^{-6} spatial variation.

Demonstrated passive stability better than 1.0×10^{-4} over one hour.

Observed coherence times exceeding six seconds using a clock transition.

Abstract

Well controlled and highly stable magnetic fields are desired for a wide range of applications in physical research, including quantum metrology, sensing, information processing, and simulation. Here we introduce a low-cost hybrid assembly of rare-earth magnets and magnetic field coils to generate a field strength of $\simeq\,10.9\,$mT with a spatial variation of less than 10$^{-6}$ within a diameter of spherical volume of $150\,$um. We characterise its tuneability and stability performance using a single Mg$^{+}$ atom confined in a radio-frequency surface-electrode trap under ultra-high vacuum conditions. The strength of the field can be tuned with a relative precision of $\leq 2\,\times\,10^{-5}$ and we find a passive temporal stability of our setup of better than $1.0\,\times\,10^{-4}$ over the course of one hour. Slow drifts on time scales of a few minutes are actively stabilised by adjusting electric currents in the magnetic field coils. In this way, we observe coherence times of electronic superposition states of greater than six seconds using a first-order field insensitive (clock) transition. In a first application, we demonstrate sensing of magnetic fields with amplitudes of $\geq0.2\,$uT oscillating at $\simeq 2\pi\,\times\,60\,$MHz. Our approach can be implemented in compact and robust applications with strict power and load requirements.