Silicon Carbide Shows How Tiny Spins Communicate

Scientists have found a way to read the spin state of a single carbon atom inside a special silicon carbide crystal.

They placed the crystal so its long axis lines up with a strong 3.4‑tesla magnet. They used special pulse tricks and a version of silicon that lacks extra isotopes. The magnetic field was set to 3.4 tesla, which is strong enough to keep the spins aligned for a long time.

The technique gave them a clear signal about 35 percent strong, letting them see the carbon’s nuclear magnetic resonance lines. They saw that the electron spin of the defect talks to carbon atoms that sit far away, in the fifth or sixth layers around the defect. At a chilly 120 K, the carbon spins wiggle in a steady rhythm, and the rhythm lasts about ten milliseconds before fading. The whole process works without needing any external labels, just the natural spin of the atoms.

A separate measurement showed a tiny coupling of five to six hertz between the nitrogen atom in the defect and the carbon atom. This means the two nuclear spins can pass information over roughly ninety milliseconds when the magnet is that strong.