Strong coupling of alkali-metal spins to noble-gas spins with an hour-long coherence time

Nuclear spins of noble gases can maintain coherence for hours at ambient conditions because they are isolated by complete electron shells¹. This isolation, however, impedes the ability to manipulate and control them by optical means or by coupling to other spin gases^2–4. Here we achieve strong coherent coupling between noble-gas spins and the optically accessible spins of an alkali-metal vapour. The coupling emerges from the coherent accumulation of stochastic spin-exchange collisions. We obtain a coupling strength ten times higher than the decay rate, observe the coherent and periodic exchange of spin excitations between the two gases and demonstrate active control over the coupling by an external magnetic field. This approach could be developed into a fast and efficient interface for noble-gas spins, enabling applications in quantum sensing and information^5,6.