Diamonds are nearly perfect crystals, but not totally perfect. The defects in these crystals give the stones their characteristic colors. But one type of defect, the NV — nitrogen-vacancy — center, can hold a particular spin, and you can change that spin with the correct application of energy. [Asianometry] explains why this is important in the video below.

Interestingly, even at room temperature, an NV center stays stable for a long time. Even more importantly, you can measure the spin nondestructively by detecting light emissions from the center.

There are obvious applications for quantum computing, but an even more practical application is sensing magnetic fields. These could replace SQUIDs, which are often used for sensitive magnetic measurements but require cold temperatures to support superconductivity.

Of course, you have to create a diamond artificially to get the NV centers the way you want and it turns out that semiconductor manufacturing tools can help produce the diamonds you need.

The last time we looked in on diamond defects, the proposal was to use them for data storage. It seems like this could be easier than holding out for room-temperature superconductors to improve SQUIDs.