Magnetic resonance techniques work by detecting the response of electronic or nuclear spins as they are manipulated by an applied magnetic field. But magnetic resonance imaging and spectroscopy remain notoriously insensitive to faint magnetic moments at small length scales. The performance of induction coils, the standard detectors, scales poorly with decreasing size, and billions of spins are required to yield a recognizable signal. In 2004 Daniel Rugar and his IBM colleagues overcame the problem by combining magnetic resonance with force microscopy. Using a chunk of cobalt at the end of a cantilever, his group was able to locate a single electron spin inside a glass slab (see PHYSICS TODAY, September 2004, page 21).
Four years later, two research groups—one led by Mikhail Lukin, Ronald Walsworth, and Amir Yacoby from Harvard University, the other led by Fedor Jelezko and Jörg Wrachtrup from the University of Stuttgart—independently demonstrated an alternative approach...
