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arXiv:2004.01057 · Physical Review Applied

Three-Dimensional Cooling of an Atom-Beam Source for High-Contrast Atom Interferometry

Jonathan M. Kwolek, Charles Fancher, Mark Bashkansky, Adam T. Black

Published Apr 22, 2020• 28 citations
arXivHTMLPDF

Abstract

We present a compact, two-stage atomic beam source that produces a continuous, narrow, collimated, and high-flux beam of rubidium atoms with sub-Doppler temperatures in three dimensions, which features very low emission of near-resonance fluorescence along the atomic trajectory. The atom-beam source originates in a pushed two-dimensional magneto-optical trap ($2{\mathrm{D}}^{+}$ MOT) feeding a slightly off-axis three-dimensional moving optical-molasses stage that continuously cools and redirects the atom beam. The capture velocity of the moving optical molasses is deliberately chosen to be low, approximately $3\phantom{\rule{0.2em}{0ex}}\mathrm{m}/\mathrm{s}$, to reduce fluorescence, and the cooling light is detuned by several atomic linewidths from resonance to reduce the absorption cross section of cooling-induced fluorescence. Near-resonance light from the $2{\mathrm{D}}^{+}$ MOT and the push beam does not propagate to the output atomic trajectory due to a ${10}^{\ensuremath{\circ}}$ bend in the atomic trajectory. The atomic beam emitted from the two-stage source has a flux up to $1.6(3)\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{0.2em}{0ex}}\mathrm{atoms}/\mathrm{s}$, with an optimized temperature of $15.0(2)\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{K}$. We employ continuous Raman-Ramsey interference measurements at the atom-beam output to study the sources of decoherence in the presence of continuous cooling, and demonstrate that the atom-beam source effectively preserves high fringe contrast even during cooling. This cold-atom-beam source is appropriate for use in atom interferometers and clocks, where continuous operation eliminates dead time, the slow atom-beam velocity (6--16 m/s) improves sensitivity, the narrow 3D velocity distribution improves fringe contrast, and the low reabsorption of scattered light mitigates decoherence caused by the continuous cooling process.

DOI
10.1103/physrevapplied.13.044057

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We present a compact, two-stage atomic beam source that produces a continuous, narrow, collimated, and high-flux beam of rubidium atoms with sub-Doppler temperatures in three dimensions, which features very low emission of near-resonance fluorescence along the atomic trajectory. The atom-beam source originates in a pushed two-dimensional magneto-optical trap (2D+2{\mathrm{D}}^{+}2D+ MOT) feeding a slightly off-axis three-dimensional moving optical-molasses stage that continuously cools and redirects the atom beam. The capture velocity of the moving optical molasses is deliberately chosen to be low, approximately 3m/s3\phantom{\rule{0.2em}{0ex}}\mathrm{m}/\mathrm{s}3m/s, to reduce fluorescence, and the cooling light is detuned by several atomic linewidths from resonance to reduce the absorption cross section of cooling-induced fluorescence. Near-resonance light from the 2D+2{\mathrm{D}}^{+}2D+ MOT and the push beam does not propagate to the output atomic trajectory due to a 10\ensuremath∘{10}^{\ensuremath{\circ}}10\ensuremath∘ bend in the atomic trajectory. The atomic beam emitted from the two-stage source has a flux up to 1.6(3)\ifmmode×\else\texttimes\fi109atoms/s1.6(3)\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{0.2em}{0ex}}\mathrm{atoms}/\mathrm{s}1.6(3)\ifmmode×\else\texttimes\fi109atoms/s, with an optimized temperature of 15.0(2)\ensuremathμK15.0(2)\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{K}15.0(2)\ensuremathμK. We employ continuous Raman-Ramsey interference measurements at the atom-beam output to study the sources of decoherence in the presence of continuous cooling, and demonstrate that the atom-beam source effectively preserves high fringe contrast even during cooling. This cold-atom-beam source is appropriate for use in atom interferometers and clocks, where continuous operation eliminates dead time, the slow atom-beam velocity (6--16 m/s) improves sensitivity, the narrow 3D velocity distribution improves fringe contrast, and the low reabsorption of scattered light mitigates decoherence caused by the continuous cooling process.
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We present a compact, single-cell atomic beam source that produces a continuous beam of rubidium atoms with cooling in three dimensions. Our design integrates an off-axis optical molasses into a two-dimensional magnetooptical trap within a single vacuum cell. The 87Rb atom beam source features a flux of 3 × 109 atoms/s, a transverse temperature of 95(5) µK, and a longitudinal temperature of 886(12) µK. We present a temporal coherence theory to evaluate the effect of longitudinal temperature on the inertial measurement performance of atom interferometers. Ultra-low light shift are verified via Raman-Ramsey interferometry, yielding a sensitivity of the center frequency to the MOT laser power is −1.653 × 10−3 Hz/mW. We hope this compact source can contribute to atom-interferometry-based inertial sensors and clocks that are both compact and sensitive.
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We study decoherence in continuously cooled atom interferometers by performing Raman-Ramsey fringe measurements in a continuous beam of 3D-sub-Doppler-cooled rubidium atoms. The atom beam is produced by a two-stage cold atom source that is designed to mitigate the decoherence of atomic interference caused by cooling induced fluorescence. The atom beam source produces a collimated beam of over 109 atoms/s that is cooled by polarization gradient cooling to temperatures as low as 14 µK. We infer the potential performance of this atom beam source in a cold-atom gyroscope and use numerical models of motion in 6 degrees of freedom to study the expected performance on dynamic platforms.
We present a cold atomic beam source based on a two-dimensional (2D)+ magneto-optical trap (MOT), capable of generating a continuous cold beam of 87Rb atoms with a flux up to 4.3*10^9 atoms/s, a mean velocity of 10.96(2.20) m/s, and a transverse temperature of 16.90(1.56) uK. Investigating the influence of high cooling laser intensity, we observe a significant population loss of atoms to hyperfine-level dark states. To account for this, we employ a multiple hyperfine level model to calculate the cooling efficiency associated with the population in dark states, subsequently modifying the scattering force. Simulations of beam flux at different cooling and repumping laser intensities using the modified scattering force are in agreement with experimental results. Optimizing repumping and cooling intensities enhances the flux by 50%. The influence of phase modulation on both the pushing and cooling lasers is experimentally studied, revealing that the mean velocity of cold atoms can be tuned from 9.5 m/s to 14.6 m/s with a phase-modulated pushing laser. The versatility of this continuous beam source, featuring high flux, controlled velocity, and narrow transverse temperature, renders it valuable for applications in atom interferometers and clocks, ultimately enhancing bandwidth, sensitivity, and signal contrast in these devices.
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