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arXiv:1502.03864 · Physical Review A

Stability of a trapped-atom clock on a chip

Ramon Szmuk, Vincent Dugrain, W. Maineult, Jakob Reichel, P. Rosenbusch

Published Jul 10, 2015• 59 citations
arXivHTMLPDF

Abstract

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 $5.8\times 10^{-13}$ at 1 s and is likely to integrate into the $1\times10^{-15}$ 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 ($5\times10^{-6}$ 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.

DOI
10.1103/physreva.92.012106

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Optically trapped ensembles are of crucial importance for frequency measurements and quantum memories but generally suffer from strong dephasing due to inhomogeneous density and light shifts. We demonstrate a drastic increase of the coherence time to 21 s on the magnetic field insensitive clock transition of (87)Rb by applying the recently discovered spin self-rephasing [C. Deutsch et al., Phys. Rev. Lett. 105, 020401 (2010)]. This result confirms the general nature of this new mechanism and thus shows its applicability in atom clocks and quantum memories. A systematic investigation of all relevant frequency shifts and noise contributions yields a stability of 2.4×10(-11)τ(-1/2), where τ is the integration time in seconds. Based on a set of technical improvements, the presented frequency standard is predicted to rival the stability of microwave fountain clocks in a potentially much more compact setup.
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.
Abstract Atomic beams are a longstanding technology for atom-based sensors and clocks with widespread use in commercial frequency standards. Here, we report the demonstration a chip-scale microwave atomic beam clock using coherent population trapping (CPT) interrogation in a passively pumped atomic beam device. The beam device consists of a hermetically sealed vacuum cell fabricated from an anodically bonded stack of glass and Si wafers. Atomic beams are created using a lithographically defined microcapillary array connected to a Rb reservoir1 and propagate in a 15 mm long drift cavity. We present a detailed characterization of the atomic beam performance (total Rb flux ≈ 7.7 × 1011 s-1 at 363 K device temperature) and of the vacuum environment in the device (pressure < 1 Pa), which is sustained using getter materials which pump residual gases and Rb vapor. A chip-scale beam clock is realized using Ramsey CPT spectroscopy of the 87Rb ground state hyperfine transition over a 10 mm Ramsey distance in the atomic beam device. The prototype atomic beam clock demonstrates a fractional frequency stability of ≈ 1.2 × 10-9/√τ for integration times τ from 1 s to 250 s, limited by detection noise. Optimized atomic beam clocks based on this approach may exceed the long-term stability of existing chip-scale clocks, and leading long-term systematics are predicted to limit the ultimate fractional frequency stability below 10-12.
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.
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 propose a compact atomic clock based on ultracold Rb atoms that are magnetically trapped near the surface of an atom microchip. An interrogation scheme that combines electromagnetically-induced transparency (EIT) with Ramsey's method of separated oscillatory fields can achieve atomic shot-noise level performance of 10^{-13}/sqrt(tau) for 10^6 atoms. The EIT signal can be detected with a heterodyne technique that provides noiseless gain; with this technique the optical phase shift of a 100 pW probe beam can be detected at the photon shot-noise level. Numerical calculations of the density matrix equations are used to identify realistic operating parameters at which AC Stark shifts are eliminated. By considering fluctuations in these parameters, we estimate that AC Stark shifts can be canceled to a level better than 2*10^{-14}. An overview of the apparatus is presented with estimates of duty cycle and power consumption.