Stability Demonstration of a 15-cc Mercury-Ion Vacuum Trap Tube

In this paper, we report our recent effort on developing a micro mercury trapped ion atomic clock. In particular, we present preliminary results of a mercury-ion clock using a 15-cc vacuum trap tube. The mercury-ion clock can achieve a short-term fractional frequency instability of 1.5 ×10 ^!12 τ ^!1/2 and reach a fractional frequency instability of 3 ×10 ^{! 14} after averaging for an hour. The clock can remain at the 10 ^!14 fractional frequency instability level up to several hours. Furthermore, the sealed 15-cc vacuum tube has demonstrated a very long ion lifetime of over two hundred days. We also investigated the mercury vapor density inside the vacuum trap tube by measuring the coherence time of the microwave clock transition.