Neutral Cesium Atoms in Strong Magnetic-Quadrupole Fields at Sub-Doppler Temperatures

Abstract

We have investigated optical capture of neutral cesium atoms by radiation pressure forces in a stiff magneticquadrupole field. Permanent magnets were used to generate field gradients ranging from 60 G/cm to more than 300 G/cm. With increasing gradient we observe a step decrease in the equilibrium number of trapped atoms but only a moderate reduction of their density. From the dynamics of the trapped atomic sample we derive temperatures as low as 40p.K or 30% of the Doppler limit even in these strong magnetic-quadrupole fields.

Counting cold collisions

“…From the measured decay constants we can directly infer the temperatures T , see Fig.4. These results are in excellent agreement with previous temperature measurements [4,8]. Extrapolating the curves to zero repump intensity and taking into account the measured trap volumes we infer values for the total collisional rate coefficients β HCC =(3.3±1.8), (4.6±1.7), (4.3±1.9)·10 −11 cm 3 s −1 for a), b) and c), respectively.…”

Cold collisions in a high-gradient magneto-optical trap

“…Cold collisions have been intensely studied in MOTs with low magnetic field gradients of order B = ∂ B/∂z ∼ 10 G cm −1 . Previous experiments performed in our group [3,4] and at Caltech [5] have shown that the dynamics of atoms trapped in a high-gradient MOT (B ∼ 100-500 G cm −1 ) is similar to that of a standard MOT. In particular, the dependence of the atomic temperature on the laser parameters is the same, because within the small trapping volume the Zeeman shift of the atomic levels is only a fraction of the natural linewidth.…”

“…Schematic overview of collisional processes in a MOT. Shown are interaction energies between two atoms in the ground and excited states S + P (resonant dipole-dipole interaction ∼ ± 1/R 3 for large R) and two ground-state atoms S + S, F = (4, 4), (4,3), (3,3) (short-range interaction, essentially flat at long distances) together with distances characteristic for resonant excitation by both MOT lasers. At very short distances around R G a change of the ground-state hyperfine structure can occur.…”

An Asymmetric Magneto-Optical Trap

“…Since the spring constant is one of the basic parameters of a MOT, there has been much effort to measure the spring constant, inferred from the measured spatial profile and the temperature by means of the equi-partition theorem (Drewsen et al, 1994;Wallace et al, 1994), by using the beam imbalance (Wallace et al, 1994;Steane et al, 1992) or by using the imposed oscillating magnetic field (Kohns et al, 1993;Hope et al, 1993). Authors in Ref.…”