Compact Optical Clock with 5×10 ⁻¹³ Instability at 1 s

We present a compact optical atomic clock design based on a two-photon transition at 778 nm in rubidium that is capable of a frequency instability of 5×10−13 at 1 s. The simple architecture occupies less than 30 L volume and currently uses commercial off-the-shelf components making this system an attractive, appealing, and competitive candidate to meet GPS-III spacecraft frequency stability requirements.