Liter sized ion clock with 10-15 stability

We have recently completed a breadboard ion-clock physics package based on Hg ions shuttled between a quadrupole and a 16-pole rf trap. With this architecture we have demonstrated short-term stability ~2-3times10^-13 at 1 second, averaging to 10^-15 at 1 day. This development shows that H-maser quality stabilities can be produced in a small clock package, comparable in size to an ultra-stable quartz oscillator required for holding 1-2times10^-13 at 1 second. This performance was obtained in a sealed vacuum configuration where only a getter pump was used to maintain vacuum. We have selected materials for the vacuum tube, ion trap and UV windows that will allow a 450 C tube bake-out to prepare for tube seal-off. This approach to the vacuum follows the methods used in flight vacuum tube electronics, such as flight TWTA´s where tube operation lifetime and shelf life of up to 15 years is achieved. We have made a thorough study of residual gas shifts of the ion-clock frequency and a study of alternate noble gasses as a buffer gas within the sealed tube. We find that neon is more suitable than the traditional use of helium, with 2-3 times less pressure induced frequency pulling. Since neon is heavier than helium, negligible diffusion losses will occur over the operation lifetime. We have developed a modular optical system that integrates lens, mirrors, ²⁰²Hg lamp and exciter, photomultiplier tube and pulse generation electronics, all into a small package that attaches to the vacuum tube, aligned with its optical ports and ion trap inside. Similarly, the reference magnetic field coil, an inner layer magnetic shield and a 40.5 GHz microwave feed with window have been incorporated into this breadboard