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

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 (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, ∼ 3 m/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 + MOT and the push beam does not propagate to the output atomic trajectory due to a 10 • bend in the atomic trajectory. The atomic beam emitted from the two-stage source has a flux up to 1.6(3)×10 9 atoms/s, with an optimized temperature of 15.0(2) µK. 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.

Atom interferometry with thousand-fold increase in dynamic range

“…Further improvement of the scheme is possible by incorporating more than two interferometric sequences within the same experimental shot, enabling the gain demonstrated here for sequential operation within a single shot. The dual-T approach may also be applied in other atom interferometers, such as gyroscopes in the butterfly configuration (36,37) and multiaxis inertial sensors in launched (38,39) or continuous (40) configurations.…”

A continuous, sub-Doppler-cooled atomic beam interferometer for inertial sensing

“…The configuration of the continuous 3D-cooled atom interferometer is shown in Figure 1. It is based on a previously demonstrated 3D-cooled 87 Rb beam combining a 2D + magneto-optical trap and a tilted moving 3D polarization gradient cooling stage [28]. The key features of the rubidium beam are sub-Doppler temperatures in 3D, dynamically controllable longitudinal velocity (6 -16 m/s), high flux (greater than 10 9 atoms/s), and relatively low downstream fluorescence emitted from the cooling stages, resulting in low decoherence in atomic interference measurements made using the cold beam.…”

“…The simplest scheme for continuous-beam atom interferometry uses a thermal atomic beam from an effusive oven, employing no laser cooling of the atoms [4,26,27]. Laser cooling of continuous atomic beams [28] makes possible increased interrogation time due to the slower mean velocity of cold atom sources, increased static fringe contrast due to the reduction in Doppler width of momentum-changing transitions, and potentially improved performance under dynamics (accelerations and rotations) due to reduction of inhomoge- * adam.black@nrl.navy.mil neous broadening of atomic phase and scale factor. Reduction of the atomic velocity width in all three dimensions is important for performance under acceleration and rotation dynamics in three dimensions [4,29,30].…”

“…The experiment does not rely on significant gravitational curvature of the atomic trajectory to reduce decoherence caused by scattered cooling light, making possible operation in arbitrary sensor orientations and under dynamics. Instead, we make use of a 3Dcooled atom-beam source designed to reduce decoherence induced by scattered light [28]. The 3D-cooled atom source is relatively compact, with a length of approximately 10 cm, enabling portable sensor applications.…”

Continuous collective strong coupling between atoms and a high finesse optical cavity

“…There is much interest in providing atoms in a continuous way [34], for example in optical tweezers [35], continuous clock measurements [36] and matter wave interferometers [37]. A continuous supply of atoms increases the sampling time and duty cycle rate, and therefore improves signalto-noise ratios and clock stability [38], reduces dead-time and aliasing [39], and gives access to new physical regimes for probing physics.…”