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 [1] has advanced from proof of concept [2] to a mature quantum technology [3], with broad fields of applications in physics, materials engineering, life-sciences, and beyond.

In this talk, I will present the founding principles and key engineering challenges in the field and highlight particularly rewarding applications of single spin-based quantum sensors. A particular focus will lie on new insights these sensors bring to mesoscopic condensed-matter physics, such as super-conductors [4] or novel magnetic materials. Here, I will focus on the use of single-spin quantum sensors to study and engineer atomically thin “van der Waals” magnets [5-7] - an emerging class of magnetically ordered systems that combine fundamental and practical interests and which 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, such as their use in studying dynamical phenomena in quantum materials [8] or their applications under extreme conditions, such as Tesla-range magnetic fields, or millikelvin temperatures, where new exciting applications wait to be explored.

[1]   B. Chernobrod and G. Berman, J. of Applied Physics 97, 014903

[2]   G. Balasubmaranian et al., Nature 455, 644; J. Maze et al., Nature 455, 644

[3]   N. Hedrich et al. P.R. Appl., 14, 64007; P. Appel et al., Rev. Sci. Instr. 87, 63703;  Qnami.com

[4]   L. Thiel et al., Nature Nanotechnology 11, 677

[5]   C. Gong and X. Zhang, Science 363, 706; M. Gibertini et al., Nature Nano. 14, 408

[6]   L. Thiel et al., Science 364, 973

[7]   F. Tabataba-Vakili et al., Nature Comm. 15, 4735;
Tschudin et al., Nature Comm. 15, 6005
C. Pellet-Mary et al. arXiv:2503.04922

[8]   J. Rovny et al., Nature Reviews Physics 6, 753