Loss of cold atoms due to collisions with residual gases in free flight and in a magneto-optical trap

Abstract

The loss rate of cold atoms in a trap due to residual gas collisions differs from that in a free state after the cold atoms are released from the trap. In this paper, the loss rate in a cold rubidium-87 atom cloud was measured in a magneto-optical trap (MOT) and during its free flight. The residual gas pressure was analyzed by a residual gas analyzer, and the pressure distribution in a vacuum chamber was numerically calculated by the angular coefficient method. The decay factor, which describes the decay behavior of cold atoms due to residual gas collisions during a free flight, was calculated. It was found that the decay factor agrees well with theoretical predictions under various vacuum conditions.

Cross-calibration of atomic pressure sensors and deviation from quantum diffractive collision universality for light particles

“…As expected, the fitted values on different dates agree with each other. We find ⟨σ tot v⟩ = [5.49(6), 5.54(7), 5.55 (8)] × 10 −15 m 3 s −1 , and i g = [0.632 (7), 0.625 (7), 0.645 (10)].…”

“…For the blue triangles, we have ⟨σtot v⟩ = 5.54(7) × 10 −15 m 3 s −1 and ig = 0.625 (7). For the green squares, we have ⟨σtot v⟩ = 5.58(6) × 10 −15 m 3 s −1 and ig = 0.645 (10). The universal fit to the combined set of data yields ⟨σtot v⟩ = 5.52(9) × 10 −15 m 3 s −1 and ig = 0.633 (10).…”

“…For the green squares, we have ⟨σtot v⟩ = 5.58(6) × 10 −15 m 3 s −1 and ig = 0.645 (10). The universal fit to the combined set of data yields ⟨σtot v⟩ = 5.52(9) × 10 −15 m 3 s −1 and ig = 0.633 (10). The universal plot of all the data (the loss rate coefficient is normalized by the value at zero trap depth and the trap depth is re-scaled by U d ) is shown in (b), and the grey dashed line represents the universal fit function.…”

“…The universal function fit to the combined data set is shown in figure 4(b). The (heating-corrected) values obtained by fitting the combined data set are ⟨σ tot v⟩ = 5.52(9) × 10 −15 m 3 s −1 and i g = 0.633 (10).…”

“…Laser cooled atoms confined in a magnetic or magneto-optical trap can be used as sensors of absolute pressure and particle flux measurements in vacuum [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. For example, the background gas density or pressure can be determined by observing loss of trapped atoms induced by collisions with ambient atoms or molecules.…”