Combined quantum-state preparation and laser cooling of a continuous beam of cold atoms

Abstract

We use two-laser optical pumping on a continuous atomic fountain in order to prepare cold cesium atoms in the same quantum ground state. A first laser excites the F = 4 ground state to pump the atoms toward F = 3 while a second π-polarized laser excites the F = 3 → F = 3 transition of the D2 line to produce Zeeman pumping toward m = 0. To avoid trap states, we implement the first laser in a 2D optical lattice geometry, thereby creating polarization gradients. This configuration has the advantage of simultaneously producing Sisyphus cooling when the optical lattice laser is tuned between the F = 4 → F = 4 and F = 4 → F = 5 transitions of the D2 line, which is important to remove the heat produced by optical pumping. Detuning the frequency of the second π-polarized laser reveals the action of a new mechanism improving both laser cooling and state preparation efficiency. A physical interpretation of this mechanism is discussed.

Magneto-optical spectroscopy with polarization-modulated light

“…Finally polarization modulation with variable duty cycle can also find applications in the preparation and manipulation of specific atomic states, i.e., in metrology [18] and in quantum information processing [19].…”

First uncertainty evaluation of the FoCS-2 primary frequency standard

“…The first PBS splits off 7.5 mW to generate the 2D-MOT pushing beam while the second PBS is used to superimpose the repumping beam with the cooling beam used in the 2D-MOT. A two-laser optical pumping method is used for the atomic state preparation |F = 3, m F = 0 [17]. The first beam is produced by the L2L tuned to the cross-over of the |F = 4 → |F = 4 − |F = 4 → |F = 5 absorption line.…”

Measurement of the magnetic field profile in the atomic fountain clock FoCS-2 using Zeeman spectroscopy

“…The longitudinal temperature at the output of the moving molasses is 75 µK. Before entering the microwave cavity, the atomic beam is collimated by transverse Sisyphus cooling and the atoms are pumped into |F = 3, m F = 0 with a state preparation scheme combining optical pumping with laser cooling [14]. After these two steps, the transverse temperature is decreased to approximately 4 µK while the longitudinal temperature stays the same.…”

“…This measurement is done in five steps. First, we prepare the atoms in |F = 3, m = 0 using a two-laser optical pumping technique [14] and consecutively transfer them into the |F = 4, m = 0 clock state with a π-interaction after a first passage through the microwave cavity. Then, we drive the ∆m = ±1 transitions with a short pulse of ac magnetic excitation (12 ms) on the whole atomic beam present in the atomic resonator.…”