Minimizing Zeeman sensitivity on optical and hyperfine transitions in EuCl3·6H2O to extend coherence times

In this paper we characterize the spin Hamiltonian and magnetic dependence of the ground and excited states of the F07→5D0 transition of EuCl3·6H2O. From this information, magnetic field values at which the optical and hyperfine transitions undergo turning points in frequency are found. At these turning points, the sensitivity of the transition to magnetic field fluctuations is reduced, which can result in longer coherence times. Based on a simple model, we estimate that coherence times at a turning point can be extended to the lifetime limit for optical transitions and approximately 1 min for hyperfine transitions in EuCl3·6H2O. We also show that substantial improvements in hyperfine coherence time can be made by fully deuterating the material to EuCl3·6D2O.