Gas-phase atoms and molecules are powerful
resources for many applications: sensors, quantum simulators, and fundamental
physics experiments. By implanting atoms in a solid host, one can achieve
higher numbers, higher densities, and superb localization, but typically at a
great cost: the properties of the implanted atoms are altered to an extent that
they are no longer experimentally useful. Notable exceptions to this rule are
NV centers in diamond, rare-earth-ion doped crystals, phosphorus donors in silicon,
and atoms and molecules in solid and superfluid helium.
We are investigating solid hydrogen as a host matrix for atoms and molecules. We grow parahydrogen crystals doped with alkali atoms, and we optically pump and detect their spin state. We have measured longitudinal spin relaxation and, surprisingly, found relaxation times longer than either solid or superfluid helium. We have measured transverse spin relaxation by both free induction decay and by spin echo. The observed spin-echo coherence time depends strongly on the density of orthohydrogen impurities, and is competitive with the best systems in the world at comparable electron spin densities. Possible applications will be discussed, and audience speculation will be solicited.