Abstract We describe three independent research directions focussed on the development of next-generation chip-scale atomic clocks, which combine small size, low power consumption and manufacturability with high frequency stability. The use of optical transitions in microfabricated vapor cells improves both short- and long-term frequency stability to near 10−13 at the cost of the added complexity of a chip-scale optical frequency comb. Chip-scale atomic beam microwave clocks have been successfully demonstrated and offer the potential for microsecond-level timing accuracy over one week. And finally, Sr vapor cells have been developed with lifetimes exceeding 250 hours and residual gas pressures below 1 Torr.
Abstract We describe three independent research directions focussed on the development of next-generation chip-scale atomic clocks, which combine small size, low power consumption and manufacturability with high frequency stability. The use of optical transitions in microfabricated vapor cells improves both short- and long-term frequency stability to near 10−13 at the cost of the added complexity of a chip-scale optical frequency comb. Chip-scale atomic beam microwave clocks have been successfully demonstrated and offer the potential for microsecond-level timing accuracy over one week. And finally, Sr vapor cells have been developed with lifetimes exceeding 250 hours and residual gas pressures below 1 Torr.
We provide an overview of our research on chip-scale atomic devices. By miniaturizing optical setups based on precision spectroscopy, we have developed small atomic sensors and atomic references such as atomic clocks, atomic magnetometers, and optical wavelength references. We have integrated microfabricated alkali vapor cells with small low-power lasers, micro-optics, and low-power microwave oscillators. As a result, we anticipate that atomic stability can be achieved with small size, low cost, battery-operated devices. Advances in fabrication methods and performance are presented.
The convergence of atomic spectroscopy, MEMS cell technologies and integrated photonics has led to the deployment of high-precision chip-scale atomic devices [1]. In this talk, we will present in-progress studies at FEMTO-ST Institute, France, for the development of microcellbased microwave and optical atomic clocks, with enhanced stability performances. In the first part, we will talk about the demonstration of CPT-based microwave cell clocks with stability at 1 day in the low 10−12 range [2], made possible thanks to the combination of advanced Ramsey-based interrogation sequences [3] and cells built with low gas permeation windows [4-5]. In the second part, we will discuss the in-progress development of a microcell-based optical frequency reference based on the two-photon transition of Rb atom at 778 nm. An encouraging short-term stability of 3 × 10−13 at 1 s and 3 × 10−14 at 100 s has been recently achieved [6]. Future studies will be briefly discussed.
We summarize activities performed at FEMTO-ST Institute and Centrale Lille/IEMN over the last years on the development of microfabricated vapor cells dedicated to atomic clocks, frequency references and sensors. Recent advances on the microcell technology are described. We have demonstrated CPT-based microwave clocks with stability in the low 10−12 range thanks to the implementation of advanced pulsed Ramsey-based interrogation sequences and cells built with low-permeation glass substrates and Al2O3 coatings. We have developed microcell optical frequency references, one based on the two-photon transition of Rb atom at 778 nm and one on saturated absorption of the 6S1/2-7P1/2 transition of Cs atom at 459 nm, with short-term stability levels in the low 10−13 range at 1 s and averaging down in the low 10−14 range after 100 s. Optically pumped magnetometers with sensitivity at the level of 100 fT/√Hz have also been demonstrated. In-progress studies, on both the cell technology and metrology aspects, are also discussed.
Atomic clocks represent the most advanced instruments for providing time-frequency standards, with increasing demand for designs that offer high frequency stability while minimizing size. Central to an atomic clock’s function is the atomic vapor cell, which serves as the quantum reference. Compared to traditional cells, wafer-level micro-electro-mechanical systems (MEMS) vapor cells enable cost-effective, scalable production and facilitate integration with silicon-based chips. In this work, we present a wafer-level MEMS vapor cell featuring an innovative silicon-glass-silicon transverse optical path structure. A single wafer is used to fabricate 24 identical atomic vapor cells, each with precise dimensions of 14 mm×14 mm×4.3 mm, ensuring scalability. We demonstrate an optical frequency standard that combines modulation transfer spectroscopy (MTS) with a MEMS vapor cell, featuring a compact design with excellent performance. This frequency standard achieves stability over averaging times of 1–400 s, with short-term stability of 2.6×10 −13 at 1 s and 5.1×10 −14 at 200 s. The laser linewidth is only 3.9 kHz, marking a substantial improvement over existing thermal standards, and opening potential applications in navigation, radar, and precision measurement. This work provides a crucial step toward the development of chip-scale optical clocks.
We have undertaken the development of a chip-scale atomic clock (CSAC) whose design goals include short-term stability, sigma(sub y)(tau=1 hour), of 1x10(exp 11) with a total power consumption of 30 mW and an overall device volume of 1 cu cm. The stringent power requirement dominates the physics package architecture, dictating a small (<5 mm(exp 3) gaseous atomic ensemble interrogated by a low-power semiconductor laser. At PTTI 2002, we reported on initial experimental investigations leading to the decision to employ the coherent population trapping (CPT) interrogation technique. This paper describes our further progress on the CSAC effort, including the development of custom vertical cavity surface emitting laser (VCSEL) sources and techniques for microfabricating miniature cesium vapor cells comprised of anodically bonded silicon and glass. Measurements of the signal contrast and linewidth of both the cesium D1 and D2 resonance transitions are compared, and frequency stability measurements of the CSAC testbed are presented.
We report on progress in the characterization of systematic shifts in chip-scale atomic beam clocks, which offer the potential for improved long-term stability relative to existing chip-scale atomic clocks. Previous work has demonstrated the key features of chip-scale atomic beam devices including the use of a microfabricated Si/glass atomic beam cell, passively maintained vacuum environment, and an integrated Rb atomic beam source. A beam clock has been realized using Ramsey coherent population trapping interrogation with a demonstrated short-term fractional frequency stability of ≈ 1.2 × 10^(-9)at 1 s of integration. In this talk, we discuss the path toward long-term stabilty in chip-scale atomic beam clocks and leading clock systematics. Chip-scale atomic beams are a new platform for quantum sensing which offer the potential for long-term stability in compact, low-power applications.