Scientists built nanoscale mirrors to trap light around atoms inside of diamond crystals. The mirrored cavities allow light to bounce back and forth up to 10,000 times, enhancing the normally weak interaction between light and the electronic spin states in the atoms. As a result, a 200-microsecond spin-coherence time was produced. The enhanced interactions and extended spin-coherence times are essential steps toward realizing quantum computing systems to solve some problems faster than conventional systems.