Laser-cooled ytterbium ion frequency standard

We report on the development of a trapped-ion, microwave frequency standard based on the 12.6 GHz hyperfine transition in laser-cooled ytterbium-171 ions. The entire system fits into a 6U 19-inch rack unit ($51\times 49\times 28$ cm) and comprises laser, electronics, and physics package subsystems. The performance of this development system is evaluated; the fractional frequency instability was measured to be $3.6\times {10}^{-12}\mathrm{/}\mathrm{\surd }\tau$ for averaging times between 30 s and 1500 s.