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IET conference proceedings.

Subsystems and design for a transportable cold ion microwave clock

M. A. Trigatzis, Ulas Sabahattin Gokay, Martin Knapp, Sean Mulholland, Peter Tsoulos, Gary I. Hockley, Chris Lucas, G. P. Barwood, Patrick Robert Gill

Published Aug 1, 2025• 0 citations
Publisher

Abstract

High performance transportable microwave atomic clocks are enablers for resilient GNSS-free timescales. We present progress towards a transportable laser-cooled ytterbium ion microwave clock. This system incorporates our recently developed multi-ion trap chamber and redesigned electronics and optics systems, offering reductions in size, weight and power, with improved performance over our previous system. The benchtop prototype version of this clock uses the new physics package design and reaches a short-term instability of 1.2 × 10−12/√τ. We present the transportable clock design as well as subsystem test results, which so far indicate that a similar performance to the benchtop version is achievable in a 3U rack-mounted package.

DOI
10.1049/icp.2025.2225

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High performance transportable microwave atomic clocks are enablers for resilient GNSS-free timescales. We present progress towards a transportable laser-cooled ytterbium ion microwave clock. This system incorporates our recently developed multi-ion trap chamber and redesigned electronics and optics systems, offering reductions in size, weight and power, with improved performance over our previous system. The benchtop prototype version of this clock uses the new physics package design and reaches a short-term instability of 1.2 × 10−12/√τ. We present the transportable clock design as well as subsystem test results, which so far indicate that a similar performance to the benchtop version is achievable in a 3U rack-mounted package.
Abstract Compact atomic clocks provide the stable, traceable timing required for 5G/6G telecom networks, for resilient operation of critical infrastructure including power grids, data centres and financial systems, and for maintaining accurate synchronisation during GNSS interruptions or outages. Microwave clocks based on caesium beam tubes have been the industry-standard rack-mounted clock for many years but are now outperformed in short-to-midterm instability by emerging technologies. Vapour cell clocks suffer from long-term drift which must be calibrated out periodically and on startup. This limits their use for long-term holdover and in applications where the device needs to operate after a cold start. Additionally, optical clocks require a narrow-linewidth clock laser and optical frequency comb. The ytterbium ion microwave clock developed at the National Physical Laboratory (NPL) does not require these subsystems and combines this relative simplicity with the benefits of laser cooling (long-term stability, accuracy). In this paper, we describe an ion trap physics package design where its functionality has been evaluated in a benchtop clock and forms the basis of a new design for a compact, transportable clock. We describe the operation and performance of the benchtop clock, demonstrating a short-term fractional frequency instability of 1.4 × 10 − 12 /√τ. The design for a new transportable clock based on this new physics package is detailed, as are the validation tests of other key subsystems.
A portable microwave clock incorporating laser-cooling of171Yb+promises to bring significantly improved performance compared to existing thermal commercial devices. We report on progress in the development of a compact microwave frequency standard designed to fit in a 19-inch rack enclosure that comprises laser, electronics and physics package subsystems. Recent results in which a local oscillator was disciplined by laser-cooled trapped171Yb+ions are presented. Preliminary measurements have demonstrated a fractional frequency instability of 1 × 10-13at 10,000 s. Potential applications include telecommunications and financial operations time reference systems as well as navigation system integrity.
Stable and accurate timekeeping is essential in today’s commercial and military applications. For decades, the 5071A Cesium beam clock has been the mainstay for long-term holdover in strategic applications for its unmatched performance. However, is too large, power hungry and cumbersome for most mobile platforms. To enable improved performance in lower size, weight and power applications, a new physics solution is required over traditional clock technology. In this paper we will present our Ytterbium microwave ion clock progress as a small form factor, high performance clock for use in military and commercial applications where portability is critical. Our device targets maximum performance improvement over traditional methods while minimizing technical risk, leveraging existing manufacturing, and targeting the lowest possible size, power and cost. The Physics Package includes a linear quadrupole trap, an electron gun (e-gun) ionizer, a passive getter pump and a Yb oven. We use electron impact ionization to load Ytterbium-171 ions which are cooled down to room temperature using buffer gas. Interaction-time limited Rabi spectroscopy using microwave radiation at 12.6 GHz is performed. The resulting microwave Rabi linewidth is used for closed-loop clock operation. Concurrent work is underway to develop a 369 nm Distributed Bragg Reflector laser which is essential for robust operation of the clock. We will discuss the specifications, the detailed design of our Ytterbium Microwave Ion Clock, the first assembled Physics Package and related preliminary test results.
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