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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Demonstration of a Mercury Trapped Ion Clock Prototype

Thai M. Hoang, Sang Kun Chung, Thanh Le, John D. Prestage, Lin Yi, Robert L. Tjoelker, Nan Yu, Sehyun Park, Sung‐Jin Park, James Gary Eden, Christopher E. Holland

Published Jul 7, 2021• 3 citations
Publisher

Abstract

In this work, we report a prototype of micro mercury trapped ion atomic clock. All the clock components have been packaged and demonstrated in a magnetic shield box of 4 liters. The prototype clock shows promising performance with a short-term fractional frequency instability below 10−11τ−12and can reach the 10−14-instability level after a day of averaging. The prototype clock is capable of reaching the10−15-fractional frequency instability range. Our demonstration of the integrated clock prototype paves the way for further SWaP reduction and maturation.

DOI
10.1109/eftf/ifcs52194.2021.9604234

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Scientific Reports•Dec 15, 2025•2 citations
In this work, we report a prototype of micro mercury trapped ion atomic clock. All the clock components have been packaged and demonstrated in a magnetic shield box of 4 liters. The prototype clock shows promising performance with a short-term fractional frequency instability below 10−11τ−12and can reach the 10−14-instability level after a day of averaging. The prototype clock is capable of reaching the10−15-fractional frequency instability range. Our demonstration of the integrated clock prototype paves the way for further SWaP reduction and maturation.
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!12τ!1/2and reach a fractional frequency instability of 3 ×10!14after averaging for an hour. The clock can remain at the 10!14fractional 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.
Micro mercury trapped ion clock prototypes with 10−14^{-14}−14 frequency stability in 1-liter packages
Modern communication and navigation systems are increasingly relying on atomic clocks. As timing precision requirements increase, demands for lower SWaP (size, weight, and power) clocks rise. However, it has been challenging to break through the general trade-off trend between the clock stability performance and SWaP. Here we demonstrate micro mercury trapped ion clock (M2TIC) prototypes integrated with novel micro-fabricated technologies to simultaneously achieve high performance and low SWaP. The M2TIC prototypes could reach the [Formula: see text]-stability level in 1 day with a SWaP of 1.1 L, 1.2 kg, and under 6 W of power. This stability level is comparable to the widely used rack-mount Microchip 5071A cesium frequency standard. These standalone prototypes survived regular commercial shipping across the North American continent to a government laboratory, where their performance was independently tested. The M2TIC sets a new reference point for SWaP and performance and opens opportunities for high-performance clocks in terrestrial and space applications.
Trapped mercury ion is a promising candidate for portable and operational atomic clocks. It operates at the 40.5GHz ground state hyperfine transition of 199Hg ions. Mercury ions are confined in a linear RF trap, buffer-gas cooled, with a long ion storage lifetime in an ultra-high vacuum enclosure without an active pump. The clock transition is optically-pumped and detected with a Hg discharge lamp without need of a laser light source. This approach has proven to provide simplicity in design and implementation and robustness in operation. In this paper, we report our recently effort on developing a micro and low-power mercury trapped ion clock in the DARPA ACES program. In a 5 mm x 10 mm linear trap (0.25 cc), we have achieved the clock fractional frequency stability of .7 × 10-12τ-1/2and reached down to 7 × 10-14after 1000 seconds of averaging. We will discuss the clock performance under different conditions and implications toward a micro mercury trapped ion clock with low power and high stability.
Mercury trapped ion clocks have demonstrated great long-term frequency stability and robustness. In this paper, we report a demonstration of an integrated 100-cc physics package in an effort to develop a micromercury trapped ion clock with high frequency stability. The physics package consists of a sealed 30-cc vacuum tube with one layer of magnetic shielding, light source, and detector assembly. A field emitter array and a 194-nm microplasma lamp were employed together with a microtrap tube to reduce the size and power consumption for a mercury trapped ion clock. We show that the 100-cc physics package is capable of providing a fractional frequency stability of 1×10−11τ−1/2 down to 5×10−14 after a few hours of integration. We also show a set of environmental sensitivity evaluations as well as the clock frequency retrace.
We describe the development and frequency instability measurements of a highly miniaturized, buffer gas cooled, trapped-ion atomic clock. The clock utilizes the 12.6 GHz hyperfine transition of the171Yb+ion. A custom-built 3 cm3vacuum package containing the ion trap is integrated with other key elements of the atomic frequency standard, including a photo multiplier tube, miniaturized laser sources at 369 nm and 935 nm, a local oscillator, and control electronics. With the clock physics package assembled on a 10 cm × 15 cm breadboard, the long-term fractional frequency instability was measured to be 6 × 10-14at 25 days of integration. Later, the clock physics package was further miniaturized, and the frequency instability was measured to be 2 × 10-11/τ1/2at integration times up to 10,000 s.
Abstract The mercury ion microwave clock is considered to be one of the leading candidates for new generation satellite navigation atomic clocks due to its excellent long-term frequency stability, extremely low frequency drift rate, high reliability and good potential for miniaturization. In recent years, the performance and maturity of the space mercury ion microwave clock have improved rapidly, and the reported long-term stability results are mostly in low 10 − 15 level. In this article, we present a compact prototype of mercury ion microwave clock aiming to spaceborne applications with the long-term stability of 10 − 16 . By regulating the physical effects contributing to the clock transition frequency shifts, the clock maintains a white frequency noise Allan deviation of 2.8×10 − 13 / τ 1/2 even with the averaging time τ over 10 5 s and achieves the long-term stability of 6.3 × 10 − 16 for averaging times of 200000 s. The space mercury ion microwave clock with such level performance will benefit the Global Navigation Satellite Systems and a wide range of space science and missions.