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European Frequency and Time Forum

The NAC - a miniature CPT Rubidium clock

Avinoam Stern, Benny Levy, Chagai Levy, Uriel Arad, Yefim Barash, Rony Mann, Alex Gorelik

Published Apr 1, 2016• 4 citations
Publisher

Abstract

Here we report of the design and characterization of a miniaturized Rubidium Frequency Standard named NAC1 (Nano Atomic Clock 1), now commercially available. Recently, the introduction of the effect of coherent population trapping (CPT) has led to a substantial reduction in power and size of commercial atomic frequency standards. Here, utilizing this effect in a traditional glass technology, we are able to introduce a compact and low power frequency standard.

DOI
10.1109/eftf.2016.7477765

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Here we report of the design and characterization of a miniaturized Rubidium Frequency Standard named NAC1 (Nano Atomic Clock 1), now commercially available. Recently, the introduction of the effect of coherent population trapping (CPT) has led to a substantial reduction in power and size of commercial atomic frequency standards. Here, utilizing this effect in a traditional glass technology, we are able to introduce a compact and low power frequency standard.
Toward the next generations of compact atomic clocks, clocks based on coherent population trapping (CPT) offer a very interesting alternative. Thanks to CPT, a quantum interfering process, this technology has made a decisive step in the miniaturization direction. Fractional frequency stability of 1.5x10-10 at 1 s has been demonstrated in commercial devices of a few cm3. The laboratory prototype presented here intends to explore what could be the ultimate stability of a CPT based device. To do so, an original double-Λ optical scheme and a pulsed interrogation have been implemented in order to get a good compromise between contrast and linewidth. A study of two main sources of noise, the relative intensity and the local oscillator (LO) noise, has been performed. By designing simple solutions, it led to a new fractional frequency limitation lower than 4x10-13 at 1 s integration. Such a performance proves that such a technology could rival with classical ones as double resonance clocks.
Rubidium atomic frequency standard(RAFS)is being used most popularly,and the miniaturization is the most significant aspect of RAFS.Cavity miniaturizing,circuits digitalizing and special function attaching are the main technical means.Coherent population trap(CPT)is a novel atomic frequency standard which can be built into a chip.Presently,the technique schemes for CPT clock include the traditional programme,adopting micro-electro-mechanical system(MEMS)technique for physical package,and adopting MEMS technique for whole set of device.Following the realization of miniaturization,the atomic frequency standard would face great development.
Miniature atomic clocks based on coherent population trapping (CPT) states in thermal atoms are an important component in many field applications, particularly where satellite frequency standards are not accessible. Cold-atom CPT clocks promise improved accuracy and stability over existing commercial technologies. Here we demonstrate a cold-atom CPT clock based on 87{}^{87}87Rb using a high-contrast double-$\ensuremath{\Lambda}$ configuration. Doppler frequency shifts are explained using a simple model and canceled by interrogating the atoms with counterpropagating light beams. We realize a compact cold-atom CPT clock with a fractional frequency stability of $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}{\ensuremath{\tau}}^{\ensuremath{-}1/2}$, thus demonstrating the potential of these devices. We also show that the long-term stability is currently limited by the second-order Zeeman shift to $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ at 1000 s.
Atomic clocks based on coherent population trapping (CPT) are of great interest for portable applications, due to their high performance, low power requirements, and potential for miniaturization. Slow frequency drift, however, limits their holdover ability on long time scales. This study reports a CPT clock that minimizes long-term drift, with a fractional frequency stability of $3\ifmmode\times\else\texttimes\fi{}{10}^{-13}$ over the span of an hour---ten times as good as previous CPT clocks. After successful shrinking of the laser-cooling apparatus, this clock could see commercial use, as the atoms fall just a few millimeters during a typical probe period.
The authors are developing chip-scale atomic clocks (CSACs) based on the85Rb coherent population trap (CPT) transition. As an intermediate milestone, we have developed a miniature atomic clock prototype. In this paper, we report on the design combing the miniature physics part, low-power digital control circuits and low-power microwave system, and the process that enable an atomic clock to be made with an overall size of 20 cm3volume, power consumption about 400 mWatts, and an Allen Deviation at 100 s of 2.9E-11.