Investigating Eu:CaSO₄ crystals for precision measurements of fundamental symmetries

New sources of time reversal (T) violation are necessary to explain phenomena beyond the Standard Model such as the matter-antimatter asymmetry of the universe. Additionally, hadronic T-violation searches for P-odd and T-odd nuclear moments could address the strong CP (charge conjugation and parity inversion) problem. Crystals doped with lanthanides such as europium are candidates for measuring T-violating nuclear moments due to the large number of dopant ions a crystal can host. In addition, the lanthanides' narrow optical transitions provide a means to control and readout their nuclear spin state. Furthermore, certain host materials can mitigate the challenges of using crystals for precision measurements, such as decoherence and inhomogeneous broadening. Calcium sulfate (CaSO4) is one such promising host crystal because its low nuclear spin density reduces decoherence for the dopant ion nuclear spins. We have observed the narrow 7F0 -> 5D0 transition of the Eu ion in four different crystallographic sites in Eu:CaSO4 and measured the T1 lifetimes. We have also manipulated hyperfine populations via persistent spectral hole burning, a milestone for T-violation searches with this material.