Evaluation of New Solid Rubidium Source Using Atomic Clock Stabilization Loop

We synthesized and evaluated rubidium azide as a new solid alkali metal source for microfabricated atomic clocks. A MEMS-based gas cell was filled with Rb as the alkali metal source for activation and a buffer gas (N
2
or Ar), and the frequency stability was evaluated by incorporating the cell into a feedback loop of the atomic clock. The pressure drift in the gas cell degrades the longterm frequency stability. It is mainly induced by physical absorption on the residue after the activation, but our source is chemically stable and produces no residue in the activation process. Consequently, we successfully confirmed a significant improvement of the long-term frequency stability compared with that of a conventional alkali metal source.