Next Generation High Stability, Long-Life Mercury Ion Clocks for Ground and Space Applications

Eric Tardiff, Eric Burt, Daphna Enzer, Vladimir Iltchenko, Andrey Matsko, Jamie McKelvy, Anatoliy Savchenkov, Robert Tjoelker, Michael Toennies, Wei Zhang

Abstract:	With its 40+ year history, mercury ion clocks have demonstrated excellent performance in both ground and space applications. The microwave-based technology has resulted in observations of mercury clocks with relative frequency stability ranging from nearly 1E-14/1E-16 (measured at 1s/1E4s, respectively) [Tjoelker et al. (1996), Dick et al. (1998), Burt et al. (2008)] in clocks with a 200L volume to 1E-11/1E-13 (measured at 1s/1E4s, respectively) in a 1L volume [Hoang et al. (2023)]. A recently completed space-based mercury ion clock technology demonstration mission (NASA Deep Space Atomic Clock (DSAC) [Tjoelker et al. (2016), Burt et al. (2021)]) had a relatively compact form factor (?19L) and proved the ability of the technology to support 5 year life with a fractional frequency stability from 2E-13 to 2E-15 (measured at 1s/1E4s, respectively) and long term drift <3E-16/day. This low drift, 1-2 orders of magnitude lower than other currently operating space clocks based on other principles, illustrates this technology’s utility for applications requiring autonomy. The relatively long clock life along with its low sensitivity to ambient temperature and magnetic field makes the device promising for future critical space (e.g. GNSS) and ground (e.g. NASA Deep Space Network) applications. We here report on targeted R&D efforts following the DSAC mission towards the development of a manufacturable clock prototype intended for future ground and flight applications that require hydrogen maser level stability performance and reliability. We present the clock concept, which is designed to reduce the clock’s size, weight and power consumption (SWaP) while still maintaining or even improving performance. We developed a new compact quadrupole ion trap configuration supporting long clock transition coherence time observations exceeding similar parameters of DSAC by an order of a magnitude. Lifetime and reliability considerations of the clock’s critical components will also be addressed. Finally, the importance of the local oscillator utilized in the clock is illustrated and a possibility of implementation of a compact mercury clock with 4E-15 to 2E-16 stability (measured at 1s/1E4s, respectively) is discussed.
Published in:	Proceedings of the 55th Annual Precise Time and Time Interval Systems and Applications Meeting January 22 - 25, 2024 Hyatt Regency Long Beach Long Beach, California
Pages:	25 - 35
Cite this article:	Tardiff, Eric, Burt, Eric, Enzer, Daphna, Iltchenko, Vladimir, Matsko, Andrey, McKelvy, Jamie, Savchenkov, Anatoliy, Tjoelker, Robert, Toennies, Michael, Zhang, Wei, "Next Generation High Stability, Long-Life Mercury Ion Clocks for Ground and Space Applications," Proceedings of the 55th Annual Precise Time and Time Interval Systems and Applications Meeting, Long Beach, California, January 2024, pp. 25-35. https://doi.org/10.33012/2024.19596
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