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Microfabricated vapor cell atomic clocks at FEMTO-ST

Clément Carlé, Martin Callejo, Andrei Mursa, Moustafa Abdel Hafiz, Quentin A. A. Tanguy, Rémy Vicarini, Jacques Millo, Vincent N. Maurice, Emmanuel Klinger, Nicolas Passilly, Rodolphe Boudot

Published Sep 30, 2024• 1 citation
OpenAlex

Abstract

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.

Related papers

Advances in microfabricated vapor cells for chip-scale atomic clocks and sensors

Andrei Mursa, G. Faure, Clément Carlé +16 more

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.

•Sep 14, 2026•0 citations

Short-term stability of a microcell optical reference based on Rb atom two-photon transition at 778 nm

Martin Callejo, Andrei Mursa, Rémy Vicarini +5 more

We report on the development and short-term stability characterization of an optical frequency reference based on the spectroscopy of the rubidium two-photon transition at 778 nm in a microfabricated vapor cell. When compared against a 778 nm reference signal extracted from a frequency-doubled cavity-stabilized telecom laser, the short-term stability of the microcell frequency standard is 3.5 $\times$ 10$^{-13}$ $τ^{-1/2}$ until 200~s, in good agreement with a phase noise level of $+$ 43 dBrad$^2$/Hz at 1~Hz offset frequency. The two main contributions to the short-term stability of the microcell reference are currently the photon shot noise and the intermodulation effect induced by the laser frequency noise. With still a relevant margin of progress, these results show the interest of this spectroscopic approach for the demonstration of high-stability miniaturized optical vapor cell clocks. Such clocks are poised to be highly beneficial for applications in navigation, communications, and metrology.

arXiv:2407.00841•Jun 30, 2024•0 citations

Short-term stability of a microcell optical reference based on the Rb atom two-photon transition at 778 nm

Martin Callejo, Andrei Mursa, Rémy Vicarini +5 more

We report on the development and short-term stability characterization of an optical frequency reference based on the spectroscopy of the rubidium two-photon transition at 778 nm in a microfabricated vapor cell. When compared against a 778 nm reference signal extracted from a frequency-doubled cavity-stabilized telecom laser, the short-term stability of the microcell frequency standard is 3.5×10−13τ−1/2 until 200 s, in good agreement with a phase noise level of +43dBrad2/Hz at 1 Hz offset frequency. The two main contributions to the short-term stability of the microcell reference are currently the photon shot noise and the intermodulation effect induced by the laser frequency noise. Retaining a relevant margin of progress, these results show the interest of this spectroscopic approach for the demonstration of high-stability miniaturized optical vapor cell clocks. Such clocks are poised to be highly beneficial for applications in navigation, communications, and metrology.

Journal of the Optical Society of America B•Nov 22, 2024•14 citations

Pulsed-CPT Cs-Ne microcell atomic clock with frequency stability below 2 × 10 −12 at 10 5 s

Clément Carlé, Moustafa Abdel Hafiz, Shervin Keshavarzi +3 more

We report on the mid-term stability progress of a table-top coherent population trapping (CPT) microcell atomic clock, previously limited by light-shift effects and variations of the cell's inner atmosphere. The light-shift contribution is now mitigated through the use of a pulsed symmetric auto-balanced Ramsey (SABR) interrogation technique, combined with setup temperature, laser power, and microwave power stabilization. In addition, Ne buffer gas pressure variations in the cell are now greatly reduced through the use of a micro-fabricated cell built with low permeation alumino-silicate glass (ASG) windows. Combining these approaches, the clock Allan deviation is measured to be 1.4 × 10 −12 at 10 5 s. This stability level at one day is competitive with the best current microwave microcell-based atomic clocks.

Optics Express•Feb 10, 2023•29 citations

Saturated absorption spectroscopy of the Cs atom 6S1/2 → 7P1/2 transition at 459 nm in a microfabricated vapor cell

Emmanuel Klinger, Andrei Mursa, C. M. Rivera-Aguilar +3 more

Microfabricated (MEMS) alkali vapor cells are at the core of high-precision integrated atomic quantum sensors and devices [1], such as microwave and optical clocks, or magnetometers. The first chip-scale atomic device was a microwave atomic clock based on coherent population trapping [2]. It has offered in its industrial and commercialized version an ultra-low size-power -instability budget, impacting a plethora of industrial and scientific applications. Nevertheless, the short-term stability of these clocks is usually limited at about 10−10 at 1 s. Hot vapor MEMS-based optical frequency standards constitute a new generation of miniaturized clocks, with enhanced stability. These references keep the benefit of using wafer-scalable and mass-producible vapor cells while preventing ultra-high vacuum technologies and laser cooling. Among the transitions explored, the 6S1/2 → 7P1/2 near-UV transition of Cs atom was used to demonstrate an optical reference with a stability of 2.1 × 10−13 at 1 s and averaging down to a few 10−14 [3]. However, this reference was based on a 5 cm-long glass-blown cell, not compliant with the advent of a fully-miniaturized and low-power optical clock. In this work [4], we present the characterization of sub-Doppler resonances detected in a microfabricated cell by probing, in a simple saturated absorption configuration, the Cs atom 6S1/2 → 7P1/2 transition at 459 nm. The impact of the laser intensity and cell temperature on the sub-Doppler resonance is experimentally investigated. Optimal values are identified for the development of a near-UV microcell-stabilized frequency reference. Detection noise measurements are also reported, predicting a short-term stability in the 10−13 range at 1 s. Tests of cells with embedded getters are under progress for improved purity of the cell inner atmosphere and narrowing of the resonance.

•Sep 30, 2024•0 citations

μ POP Clock: A Microcell Atomic Clock Based on a Double-Resonance Ramsey Scheme

Etienne Batori, C. Affolderbach, Matthieu Pellaton +5 more

We demonstrate and study a microcell microwave atomic clock based on optical-microwave double resonance (DR) interrogation operated in a pulsed Ramsey scheme, called the \ensuremath{\mu}POP clock, based on a microfabricated Rb vapor cell and a micro-loop-gap microwave resonator. For the mm-scale dimensions of this cell, the population and coherence relaxation rates of the Rb clock transition are on the order of 4--5 kHz, which puts constraints on the useful Ramsey times and overall pulse sequence in view of optimized clock performance. Our proof-of-principle demonstration of the \ensuremath{\mu}POP clock shows that the pulsed DR approach is nevertheless feasible and results in a short-term clock stability of 1 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}11}$ \ensuremath{\tau}${}^{\ensuremath{-}1/2}$ and reaching the \ensuremath{\le}2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}12}$ level at timescales of 1000 s to one day. The short-term instability budget established for the \ensuremath{\mu}POP clock shows that the main limitation to the short-term stability arises from the detection noise. Thanks to the pulsed Ramsey scheme, light-shift effects are strongly reduced in the \ensuremath{\mu}POP clock, which opens perspectives for further improvements of long-term clock stability, in view of future generations of miniature vapor-cell clocks with enhanced performances based on the DR scheme.

Physical Review Applied•Nov 14, 2022•30 citations
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.
We report on the development and short-term stability characterization of an optical frequency reference based on the spectroscopy of the rubidium two-photon transition at 778 nm in a microfabricated vapor cell. When compared against a 778 nm reference signal extracted from a frequency-doubled cavity-stabilized telecom laser, the short-term stability of the microcell frequency standard is 3.5 ×\times× 10−13^{-13}−13 τ−1/2τ^{-1/2}τ−1/2 until 200~s, in good agreement with a phase noise level of +++ 43 dBrad2^22/Hz at 1~Hz offset frequency. The two main contributions to the short-term stability of the microcell reference are currently the photon shot noise and the intermodulation effect induced by the laser frequency noise. With still a relevant margin of progress, these results show the interest of this spectroscopic approach for the demonstration of high-stability miniaturized optical vapor cell clocks. Such clocks are poised to be highly beneficial for applications in navigation, communications, and metrology.
We report on the development and short-term stability characterization of an optical frequency reference based on the spectroscopy of the rubidium two-photon transition at 778 nm in a microfabricated vapor cell. When compared against a 778 nm reference signal extracted from a frequency-doubled cavity-stabilized telecom laser, the short-term stability of the microcell frequency standard is 3.5×10−13τ−1/2 until 200 s, in good agreement with a phase noise level of +43dBrad2/Hz at 1 Hz offset frequency. The two main contributions to the short-term stability of the microcell reference are currently the photon shot noise and the intermodulation effect induced by the laser frequency noise. Retaining a relevant margin of progress, these results show the interest of this spectroscopic approach for the demonstration of high-stability miniaturized optical vapor cell clocks. Such clocks are poised to be highly beneficial for applications in navigation, communications, and metrology.
We report on the mid-term stability progress of a table-top coherent population trapping (CPT) microcell atomic clock, previously limited by light-shift effects and variations of the cell's inner atmosphere. The light-shift contribution is now mitigated through the use of a pulsed symmetric auto-balanced Ramsey (SABR) interrogation technique, combined with setup temperature, laser power, and microwave power stabilization. In addition, Ne buffer gas pressure variations in the cell are now greatly reduced through the use of a micro-fabricated cell built with low permeation alumino-silicate glass (ASG) windows. Combining these approaches, the clock Allan deviation is measured to be 1.4 × 10 −12 at 10 5 s. This stability level at one day is competitive with the best current microwave microcell-based atomic clocks.
Microfabricated (MEMS) alkali vapor cells are at the core of high-precision integrated atomic quantum sensors and devices [1], such as microwave and optical clocks, or magnetometers. The first chip-scale atomic device was a microwave atomic clock based on coherent population trapping [2]. It has offered in its industrial and commercialized version an ultra-low size-power -instability budget, impacting a plethora of industrial and scientific applications. Nevertheless, the short-term stability of these clocks is usually limited at about 10−10 at 1 s. Hot vapor MEMS-based optical frequency standards constitute a new generation of miniaturized clocks, with enhanced stability. These references keep the benefit of using wafer-scalable and mass-producible vapor cells while preventing ultra-high vacuum technologies and laser cooling. Among the transitions explored, the 6S1/2 → 7P1/2 near-UV transition of Cs atom was used to demonstrate an optical reference with a stability of 2.1 × 10−13 at 1 s and averaging down to a few 10−14 [3]. However, this reference was based on a 5 cm-long glass-blown cell, not compliant with the advent of a fully-miniaturized and low-power optical clock. In this work [4], we present the characterization of sub-Doppler resonances detected in a microfabricated cell by probing, in a simple saturated absorption configuration, the Cs atom 6S1/2 → 7P1/2 transition at 459 nm. The impact of the laser intensity and cell temperature on the sub-Doppler resonance is experimentally investigated. Optimal values are identified for the development of a near-UV microcell-stabilized frequency reference. Detection noise measurements are also reported, predicting a short-term stability in the 10−13 range at 1 s. Tests of cells with embedded getters are under progress for improved purity of the cell inner atmosphere and narrowing of the resonance.
We demonstrate and study a microcell microwave atomic clock based on optical-microwave double resonance (DR) interrogation operated in a pulsed Ramsey scheme, called the \ensuremath{\mu}POP clock, based on a microfabricated Rb vapor cell and a micro-loop-gap microwave resonator. For the mm-scale dimensions of this cell, the population and coherence relaxation rates of the Rb clock transition are on the order of 4--5 kHz, which puts constraints on the useful Ramsey times and overall pulse sequence in view of optimized clock performance. Our proof-of-principle demonstration of the \ensuremath{\mu}POP clock shows that the pulsed DR approach is nevertheless feasible and results in a short-term clock stability of 1 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}11}$ \ensuremath{\tau}${}^{\ensuremath{-}1/2}$ and reaching the \ensuremath{\le}2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}12}$ level at timescales of 1000 s to one day. The short-term instability budget established for the \ensuremath{\mu}POP clock shows that the main limitation to the short-term stability arises from the detection noise. Thanks to the pulsed Ramsey scheme, light-shift effects are strongly reduced in the \ensuremath{\mu}POP clock, which opens perspectives for further improvements of long-term clock stability, in view of future generations of miniature vapor-cell clocks with enhanced performances based on the DR scheme.