Operating a 171 Yb + Microwave Ion Clock in a Continuous Mode

We are developing a highly miniaturized 171 Yb + ion clock that operates in a continuous microwave-optical double-resonance mode by continuously probing the 12.6 GHz hyperfine transition in the 171 Yb + ion. In the continuous mode, the clock will not require optical shutters and electrical switches, minimizing the components of the clock. Here, we demonstrate operating the ion clock with ions trapped in a permanently sealed, passively pumped vacuum package 3 cm 3 in volume. With resonant 369-nm light continuously illuminating the ions, the light shift is a substantial systematic shift of the hyperfine ground state that must to be well characterized and controlled. We present measurements of the liaht shift and demonstrate clock frequency instabilities below $1\times10^{-12}$ at 100 s of averaging.