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IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control

Preliminary results of the trapped atom clock on a chip

Clément Lacroûte, Friedemann Reinhard, F. Ramírez-Martínez, Christian Deutsch, T. Schneider, Jakob Reichel, P. Rosenbusch

Published Jan 1, 2010• 20 citations
Publisher

Abstract

We present an atomic clock based on the interrogation of magnetically trapped (87)Rb atoms. Two photons, in the microwave and radiofrequency domain, excite the clock transition. At a magnetic field of 3.23 G the clock transition from |F = 1, m(F) = -1> to |F = 2, m(F) = 1> is 1st-order insensitive to magnetic field variations. Ramsey interrogation times longer than 2 s can be achieved, leading to a projected clock stability in the low 10(-13) at 1 s for a cloud of 10(5) atoms. We use an atom chip to cool and trap the atoms. A coplanar waveguide is integrated to the chip to carry the Ramsey interrogation signal, making the physics package as small as (5 cm)(3). We describe the experimental setup and show preliminary Ramsey fringes of line width 1.25 Hz.

DOI
10.1109/tuffc.2010.1385

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We present an atomic clock based on the interrogation of magnetically trapped (87)Rb atoms. Two photons, in the microwave and radiofrequency domain, excite the clock transition. At a magnetic field of 3.23 G the clock transition from |F = 1, m(F) = -1> to |F = 2, m(F) = 1> is 1st-order insensitive to magnetic field variations. Ramsey interrogation times longer than 2 s can be achieved, leading to a projected clock stability in the low 10(-13) at 1 s for a cloud of 10(5) atoms. We use an atom chip to cool and trap the atoms. A coplanar waveguide is integrated to the chip to carry the Ramsey interrogation signal, making the physics package as small as (5 cm)(3). We describe the experimental setup and show preliminary Ramsey fringes of line width 1.25 Hz.
We present an atomic clock based on the interrogation of magnetically trapped87Rb atoms. Two photons, in the microwave and radiofrequency domain excite the clock transition. At a magnetic field of 3.23 G the clock transition from |F=1, mF=-1rang to |F=2, mF=1rang is 1storder insensitive to magnetic field variations. Long Ramsey interrogation times can thus be achieved, leading to a projected clock stability in the low 10-13at 1 s. We use an atom chip to cool and trap the atoms. A coplanar waveguide has been integrated to the chip to carry the Ramsey interrogation signal, making the physics package as small as (5 cm)3. We describe the experimental setup and show preliminary Ramsey fringes of line width 1.25 Hz.
A portable cold87Rb atomic clock is under development at NIM. The clock uses87Rb atoms which are trapped and cooled in a small three-dimensional magneto-optical trap (3D-MOT) chamber. Within the 3D-MOT chamber, the free-falling atoms are prepared in∣F=2,mF=0⟩\vert F=2, m_{F}=0\rangle∣F=2,mF​=0⟩clock state with optical pumping (OP) directly after post cooling by2−2′2-2^{\prime}2−2′OP light and repumping. Following optical state selection, the free-falling atoms enter a microwave cavity where they undergo microwave interrogation. Eventually, the number of atoms in two clock states are detected individually by the fluorescence detection method in the detection chamber. The preliminary results show that, the selected atom number has been improved about 3 times with the optical state selection compared to the microwave state selection method. And a Ramsey fringe has been obtained experimentally, and the contrast of the central Ramsey fringe exceeds 88% with a full width half maximum (FWHM) of less than 9 Hz.
We present results from an atomic clock that employs a beam of cold 87Rb atoms and spatially separated (Ramsey) coherent population trapping interrogation of the hyperfine clock transition at 6.834 GHz. The cold atomic beam is generated through the use of a 2D+-magneto-optical trap. The interrogation is performed on the D2 line of 87Rb, and the optical fields use a counter-propagating σ+–σ− probing scheme. The use of cold atoms allows for relatively narrow Ramsey fringes even for a small spatial separation between the two interrogation zones (4.6 cm). The resulting clock has a short-term stability of 3×10−11/τ.
We demonstrate a Ramsey-type microwave clock interrogating the 6.835 GHz ground-state transition in cold [Formula: see text]Rb atoms loaded from a grating magneto-optical trap (GMOT) enclosed in an additively manufactured loop-gap resonator microwave cavity. A short-term stability of [Formula: see text] is demonstrated, in reasonable agreement with predictions from the signal-to-noise ratio of the measured Ramsey fringes. The cavity-grating package has a volume of [Formula: see text]67 cm[Formula: see text], ensuring an inherently compact system while the use of a GMOT drastically simplifies the optical requirements for laser cooled atoms. This work is another step towards the realisation of highly compact portable cold-atom frequency standards.
Abstract A sample of laser cooled atoms are created inside an additively manufactured loop-gap microwave cavity using a grating magneto-optic trap requiring only a single laser cooling beam. Using a Ramsey excitation scheme with free evolution times of up to 20 ms and based on the 87Rb ground-state clock transition, we demonstrate a short-term stability of 1.5×10−11 τ −1/2, averaging down to 2×10−12 after 100 s. The short-term stability limit is found to be dominated by the signal to noise ratio of the Ramsey fringes while for longer timescales the limitation is magnetic field noise due to the experiment being magnetically unshielded. Potential improvements to the setup and its operation point to a viable route forward for a miniaturised atomic microwave clock.
We present a compact atomic clock interrogating ultracold 87Rb magnetically trapped on an atom chip. Very long coherence times sustained by spin self-rephasing allow us to interrogate the atomic transition with 85% contrast at 5 s Ramsey time. The clock exhibits a fractional frequency stability of 5.8×10−135.8\times 10^{-13}5.8×10−13 at 1 s and is likely to integrate into the 1×10−151\times10^{-15}1×10−15 range in less than a day. A detailed analysis of 7 noise sources explains the measured frequency stability. Fluctuations in the atom temperature (0.4 nK shot-to-shot) and in the offset magnetic field (5×10−65\times10^{-6}5×10−6 relative fluctuations shot-to-shot) are the main noise sources together with the local oscillator, which is degraded by the 30% duty cycle. The analysis suggests technical improvements to be implemented in a future second generation set-up. The results demonstrate the remarkable degree of technical control that can be reached in an atom chip experiment.