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Session P5a: Present and Future Clocks for Space

Integrated Rackmount Optical Clocks
M. Ledbetter, J. Roslund, A. Cingoz, A. Kowligy, W. Lunden, G. Partridge, D. Sheredy, F. Roller, G. Skulason, J. Song, E. Atchison, O. Husain, P. Carney, MK Pasha, A. Rakholia, A. Dowd, J. Abo-Shaeer, M. Boyd, Vector Atomic
Location: Beacon B
Alternate Number 1

Vector Atomic has recently developed and fielded rackmount iodine optical clocks. The clocks are based on a robust vapor cell architecture that provides excellent short-term instability, uses no consumables, requires no laser cooling or trapping, no cavity or vacuum subsystems, and is insensitive to platform motion. Environmental systematics such as magnetic fields, light shifts and collisions are relaxed in comparison to alkali vapor cell clocks, enabling excellent performance to be maintained in field applications. Iodine clocks can provide maser-level performance in a compact, robust, and mobile package.
Our first-generation rackmount clocks were characterized at NIST for 34 days and at sea for 20 days [1], demonstrating use in the field. Short-term instability of 5x10^-14 at 1 s and long-term drifts in the low 10^-20/s were shown in each case. On intermediate timescales the clocks flicker in the low 10^-15s, with only minor degradation at sea due to larger temperature variation. Ship motion did not impact the clock performance.
Here we report results on our second-generation rackmount iodine clocks. These clocks have reduced size, weight, and power (SWaP), and improved short-term performance compared to our first-generation clocks. The clocks are fully integrated into 3U form factor, with a SWaP of 29 liters, 20 kg and 80 Watts, respectively. The integrated frequency comb provides 10 MHz and 100 MHz microwave outputs for clock and low phase noise RF applications. Comb and 1064 nm laser outputs are provided as optical links to the end user. Short-term instability is < 2.5 x 10^-14 at 1 s; the clocks typically hold < 3 x 10^-15 at 10^5 s without decorrelation or drift removal. The short-term instability and phase noise outperform high-performance active masers that typically operate in large (~1,000 L) environmental chambers. The form factor matches commercially available Cs clocks.
Characterization of first- and second-generation rackmount iodine clocks will be presented, in addition to field demonstrations and commercialization activities.
1. Jonathan Roslund et. al, “Optical clocks at Sea,” arXiv: 2308.12457 (2023).

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