Gas-phase atoms and molecules are powerful experimental resources for many applications. By implanting atoms in a solid host, one can achieve higher numbers, higher densities, and better localization than the gas phase, 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 have grown parahydrogen crystals doped with alkali atoms, and optically pumped and detected their spin state. We have measured their longitudinal spin relaxation and found T1 times longer than either solid or superfluid helium. We have measured transverse spin relaxation by both free induction decay (T2*) and by spin echo (T2), and found results competitive with the state-of-the-art. The physics limiting T2 and T2* will be discussed; applications in precision measurement and in nano-MRI will be proposed.