A three-dimensional scanning trapped-ion probe

The performance of a wide range of physical systems suffers from undesired fields from nearby surfaces, placing a premium on developing methods for understanding these imperfections. Trapped ions excel at sensing surface electric fields, but spatial scanning was limited to linear translations in previous work using radio-frequency traps, restricting the conclusions that could be drawn. Here, we demonstrate a single ion sensor confined using only static fields, consequently allowing three-dimensional position scanning and the possibility to isolate the trap from external noise. We measure static and time-varying electric and magnetic fields at distances between 50 and 450 micrometers from the metallic trap surface over a 200 micrometer-by-200 micrometer area, which we use to map charge distributions and surface noise, as well as to comprehensively discriminate between different noise sources. This approach opens up the potential to study a wide variety of materials, surface constitutions, and geometries, expanding the tool set of surface science.