Quantum two-level systems offer attractive opportunities for sensing and imaging – especially at the nanoscale. In the almost twenty years since its inception, this idea has advanced from proof of concept to a mature quantum technology with a broad field of applications in physics, materials engineering, life sciences, and beyond. 

 

In this colloquium, I will present the founding principles and key engineering challenges in the field and highlight particularly rewarding applications of single quantum sensors. A special focus will lie on new insights these sensors bring to mesoscopic condensed-matter physics. Specifically, I will discuss the use of single-spin quantum sensors to study atomically thin “van der Waals” magnets  – an emerging class of magnetically ordered systems that combine fundamental and practical interests and that so far were notoriously hard to address due to their weak magnetization and nanoscale spin-textures.

 

I will conclude with an outlook on future developments of quantum sensors, including quantum sensors operating under extreme conditions, such as high magnetic fields or millikelvin temperatures, where new exciting applications wait to be explored.