Inside every diamond are tiny magnetic needles: the nuclei of carbon atoms. Normally they point in random directions, so their signal is very weak. But if you spin diamond dust at an angle of 54.74° to the magnetic field while shining a green laser on it, the needles start to align. The signal gets hundreds of times stronger.
The secret lies in diamond defects where a nitrogen atom sits next to a vacancy. These defects, called NV centers, become polarized under light, meaning their electrons all get the same spin direction. This polarization then transfers to neighboring carbon-13 nuclei. Previously, this transfer required microwave pulses, but now the spinning sample does all the work.
In the experiment, two types of diamond particles were used: small ones enriched in carbon-13 and larger ones with natural abundance. They were spun at up to 6000 revolutions per second and illuminated with a laser. The signal was amplified 411-fold for the natural sample and 280-fold for the enriched one. That is nearly ten times better than previous attempts.
Now the researchers want to transfer this polarization to molecules attached to the diamond particle surfaces. For that, they need particles smaller than 30 nanometers. Then diamond dust could amplify signals not only from its own nuclei but also from any substance applied to it.
The angle of 54.74° between the rotation axis and the magnetic field is called the magic angle because it nullifies dipole-dipole interactions between nuclei. It is this angle that made more than 99.9% of NV centers pass through the required level crossing points twice per rotor revolution.