Long-Term Stability Analysis Towards < 10-14 Level for a Highly Compact POP Rb Cell Atomic Clock

We analyze the main effects that limit the frequency stability of a high-performance compact Rb vapor-cell atomic clock on medium- to long-term timescales up to one day, in view of identifying the fundamental clock stability limits. The clock is operated in a pressure-stabilized environment to reduce the impact of atmospheric pressure fluctuations to below 10
^-14
which allows the evaluation of the other limiting effects at this level. The current clock stability reaches 1 × 10
^-14
at 10
⁴
s averaging time, with light intensity fluctuations at the vapor cell input identified as the main contribution to the instability.