$\delta$-kick cooling using the Ioffe-Pritchard potential

We demonstrated $\delta$-kick cooling of sodium atoms with a three-dimensional anisotropic harmonic potential. The radius and temperature of the atomic cloud oscillated with kick time, indicating that the elongated atomic distribution in phase space rotates in the Ioffe-Pritchard potential. The temperature of kicked atoms was reduced to below the recoil temperature.

Figure 1

Atomic distributions in phase space. (a) Gaussian distribution in position and momentum axes for trapped atoms, (b) elongated distribution after free expansion, and (c) distribution rotated after atoms were kicked.

Figure 2

Radius of the atomic cloud vs time after atoms were released from a trap potential. The circles denote the polarization-gradient-cooled atoms, and the squares and triangles denote the kicked atoms. The kick times were (a) $2.2\mathrm{ms}$ for the squares and (b) $2.9\mathrm{ms}$ for the triangles.

Figure 3

Kick time dependence of radius and temperature of the atomic cloud. (a) and (b) The squares denote the temperature depending on kick time. (c) and (d) The circles denote the radius depending on kick time. Atomic states were (a) and (c) $F=1$, and (b) and (d) $F=2$. The solid lines were fitted to experimental data.

Figure 4

Temperature vs free expansion time $t_{\mathit{\text{free}}}$. The circles denote the experimental result. The solid line was fitted to the experimental data using Eq. (1). With increasing $t_{\mathit{\text{free}}}$, the temperature decreased. The dashed line denotes the limit due to the recoil effect in conventional laser cooling.

Figure 5

Atomic distribution kicked at $t_{\mathit{\text{free}}}=22\mathrm{ms}$. (a) Absorption imaging of polarization-gradient-cooled and $\delta$-kicked atoms. $\delta$-kicked atoms were observed for $40\mathrm{ms}$ in free expansion. (b) The radius of the atomic cloud vs time after the atoms were released from a trap potential. The circles denote the polarization-gradient-cooled atoms and the squares denote the kicked atoms.