By measuring how atoms oscillate in a magnetic field we have learnt a huge amount of chemistry using nuclear magnetic resonance machines, and they have been adapted to form Magnetic Resonance Imaging machines which are the MRI machines that allow doctors to study the soft parts of the body by using the way atoms oscillate to measure the magnetic field they are sitting in. These are incredibly useful because the electrons around the atom and even the electrons in the neighbouring atoms can affect this. This information is very useful, but the smallest object you can distinguish is about a mm.
Shimon Kolkowitz from Harvard, and colleagues are aiming for something better. Rather than using at atom as a magnetic resonator, to measure the magnetic field, they have used a mechanical resonator - effectively a microscopic tuning fork - with a tiny magnet on the end. they mounted it on a magnetic force microscope, which scans the resonator across a surface with a sub-atomic precision.
The local magnetic field will affect the vibration of the resonator which can be measured and if it comes near an atom which is vibrating at a similar frequency the interaction gets even stronger. They have used this machine to measure magnetic interactions with a single nitrogen atom in diamond, and they have even used the mechanical oscillator to affect the state of the atom and alter how it interacts with light.
This is still a very experimental machine, but they suggest it could be developed into a way of measuring and writing the state of a single quantum mechanical system, which would be useful for quantum computing, or possibly even into an MRI which would be able to see individual atoms on the outside of a molecule, and tell you what they were, and what state they are in.