In a boron nitride crystal, the perfect atomic lattice is sometimes disrupted: an atom is missing here, or replaced by a foreign one there. Under a powerful microscope, these tiny imperfections appear as traps for electrons: they capture particles and start to emit light, and they also respond to magnetic fields. It is precisely such defects that promise to become the foundation for quantum technologies operating at ordinary room temperature, without bulky refrigerators.

For a long time, it was believed that each defect was a loner. But supercomputer calculations revealed a different picture: defects often live in pairs, like two communicating vessels. One of them is a donor with an extra electron, the other is an acceptor that lacks an electron. The electron jumps from the donor to the acceptor, and the distance between them determines everything: the color of the emitted light, its brightness, and how long it lasts. By changing this distance, one can tune the quantum properties of the pair, as if turning a tuning knob.

When there are many such pairs in the crystal, they begin to influence each other, creating entire ensembles. This explains why different laboratories obtained such contradictory results: researchers were seeing the emission not of individual defects but of entire collectives, where each pair contributed its share. Now, with this knowledge, one can not guess but precisely design the desired configurations of defects — for example, to obtain a perfectly stable source of single photons for quantum communication.