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Optical and Quantum Sensing and Precision Metrology II

Industrial 171Yb+ single-ion optical clock with systematic uncertainty below 2×10^−17

J. Stühler, A. Friedenauer, P. Thoumany, Christoph Tresp, D. Heinrich, Stephan Ritter

Published Mar 5, 2026• 1 citation
Publisher

Abstract

We present the setup of our optical frequency standard (OFS) “TOPTICLOCK”. It is based on the 2S1/2 (F=0) – 2D3/2 (F=2) electric quadrupole transition at 435.5 nm of a single laser-cooled and trapped 171Yb+ ion. All required subsystems are contained in two transportable 19” rack compartments. By comparing it with a laboratory-style OFS of the German National Metrology Institute (PTB), which operates on the 467 nm electric octupole transition, using a TOPTICA DFC optical frequency comb, a frequency instability of 5×10-15/√τ with systematic uncertainty below 2×10-17 was demonstrated. The performance of TOPTICLOCK was also benchmarked by directly comparing it to another OFS operating also at the 435.5 nm clock transition. An agreement between both systems with a total uncertainty well below 10-17 was obtained.

DOI
10.1117/12.3101264

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We present the setup of our optical frequency standard (OFS) “TOPTICLOCK”. It is based on the 2S1/2 (F=0) – 2D3/2 (F=2) electric quadrupole transition at 435.5 nm of a single laser-cooled and trapped 171Yb+ ion. All required subsystems are contained in two transportable 19” rack compartments. By comparing it with a laboratory-style OFS of the German National Metrology Institute (PTB), which operates on the 467 nm electric octupole transition, using a TOPTICA DFC optical frequency comb, a frequency instability of 5×10-15/√τ with systematic uncertainty below 2×10-17 was demonstrated. The performance of TOPTICLOCK was also benchmarked by directly comparing it to another OFS operating also at the 435.5 nm clock transition. An agreement between both systems with a total uncertainty well below 10-17 was obtained.
We describe experimental investigations on an optical frequency standard based on a single laser cooled 171Yb+ ion confined in a radiofrequency Paul trap. The 435.5 nm electric-quadrupole transition from the 2S1/2(F=0) groudn state to the 2D3/2(F=2) state is probed using a diode laser system whose short-term frequency stability is derived from an environmentally isolated ULE cavity. The transition is resolved with a Foruier-limited full halfwidth of approximately 30 Hz. The absolute optical transition frequency is determined using a femtosecond frequency comb generator and a Cs fountain clock as the frequency reference. The measured frequency value is 688 358 979 321 Hz at an ambient blackbody radiation field of 300 K. The 1σ fractional uncertainty of this frequency measurement is 1×10-14.
We report on a transportable and easy-to-operate optical clock utilizing the 2S1/2 - 2D3/2 transition of a single trapped 171Yb+ ion at 436 nm. Developed within a pilot project for quantum technology in Germany lead by industry, the clock is set up in two 19″ racks. In this way, transportation can easily be realized, and the large degree of automatization allows for operation outside highly specialized laboratories for applications beyond basic research. Comparisons to existing high-accuracy optical clock systems enable a verification of the clock's stability and uncertainty budget at the low 10−17 level. During these tests, operation with 99.8% availability over more than 14 days has been achieved.
Forbidden transitions in single trapped ion systems are being considered as references for future optical frequency standards. These standards are expected to have application as highly stable and reproducible optical clocks, realizations of the metre and as optical frequency standards in their own right. This paper prescribes the work carried out at the National Physical Laboratory over recent years to use a highly forbidden 2S1/2 - 2F7/2 467 nm electric octupole transition in a single ion of 171Yb+ as a frequency reference. A review of the previous measurements needed to the locate octupole transition in this 171-isotope is given and a more detailed discussion of recent work is presented. This includes spectroscopy of the octupole transition with kilohertz resolution and a direct measurement of its optical frequency. Measurements of the dynamic Stark and the quadratic Zeeman shifts on the octupole frequency are also discussed.
The171Yb+ion possesses two transitions that are applicable as references for optical frequency standards and several general features make this ion attractive: All relevant radiations for cooling and excitation can be generated from diode lasers. A nuclear spin of 1/2 ensures a simple sublevel structure. Long storage times of Yb+in ion traps are easily obtained. The2S1/2(F = 0) →2D3/2(F = 2, mF= 0) electric quadrupole transition at 436 nm with a natural linewidth of 3.1 Hz provides a quantum noise limited instability of a single-ion frequency standard of about 2 × 10-15in 1 s. The electric octupole transition2S1/2(F = 0)→2F7/2(F = 3, mF= 0) at 467 nm with a natural linewidth in the nHz range will allow to surpass that instability level. It also possesses a lower sensitivity to field-induced frequency shifts. In this system the Fourier-limited interrogation linewidth can be adapted to that of the best available laser sources, which are presently at the level below 1 Hz. Both transitions have been recommended as secondary representations of the SI second.
Optical frequency standards based on narrow absorptions in laser-cooled single trapped ions have recently begun to demonstrate stabilities that are competitive with cold atom fountain microwave standards. This paper presents a short review of the wider state-of-the-art development of these single cold trapped ion frequency standards, coupled with a more detailed account of recent results achieved at National Physical Laboratory in respect of single ion systems based on 88Sr+, 87Sr+ and 171Yb+. Narrow linewidth data for the optical clock quadrupole and octupole transitions respectively at 674 nm in 88Sr+ and 467 nm in 171Yb+, are presented, together with a discussion of current systematics and future projections. The potential for optical clock operation is outlined.