https://phys.org/news/2018-07-tuning-quantum-scientists-frequency-precision.html

The researchers built two qubits—one an engineered molecule consisting of two phosphorus atoms with a single electron, and the other a single phosphorus atom with a single electron—and placed them just 16 nanometres apart in a silicon chip.

By patterning a microwave antenna above the qubits with precision alignment, the qubits were exposed to frequencies of around 40GHz. The results showed that when changing the frequency of the signal used to control the electron spin, the single atom had a dramatically different control frequency compared to the electron spin in the molecule of two phosphorus atoms.