Crossed Dipole Trap Research Articles

Loading a dipole trap from an atomic reservoir

Loading a dipole trap from an atomic reservoir is considered to be an efficient method for the preparation of trapped atoms at high density, which has led to notable results for the case of Rb and Cr atoms. It was also theoretically predicted to provide efficient loading also in the cesium case. In this article, we report on the experimental study of the loading of a single-arm and of a crossed dipole trap for cesium atoms. This study is performed by comparing several types of reservoirs from which the atoms are loaded: a magnetic trap, a Dark-SPOT and a compressed MOT. In all cases the number of atoms is found to decrease shortly after the beginning of the loading process. A few possible phenomena leading to such a behavior, namely the limited reservoir lifetime and/or a possible heating in the reservoir, are discussed. The loading dynamics is fitted by a phenomenological rate equation. From an experimental point of view, the reservoir loading method can be considered efficient in terms of number of transferred atoms for the single arm dipole trap. On the contrary, it does not seem to provide, for the case of cesium atoms in a crossed dipole trap, an attractive alternative in comparison with existing loading methods such as Raman sideband cooling.

Bose-Einstein Condensation of Alkaline Earth Atoms:Ca40

We have achieved Bose-Einstein condensation of ;{40}Ca, the first for an alkaline earth element. The influence of elastic and inelastic collisions associated with the large ground-state s-wave scattering length of ;{40}Ca was measured. From these findings, an optimized loading and cooling scheme was developed that allowed us to condense about 2 x 10;{4} atoms after laser cooling in a two-stage magneto-optical trap and subsequent forced evaporation in a crossed dipole trap within less than 3 s. The condensation of an alkaline earth element opens novel opportunities for precision measurements on the narrow intercombination lines as well as investigations of molecular states at the ;{1}S-;{3}P asymptotes.

Molecular Bose–Einstein condensation in a versatile low power crossed dipole trap

We produce Bose–Einstein condensates of 6Li2 molecules in a low power (22 W) crossed optical dipole trap. Fermionic 6Li atoms are collected in a magneto-optical trap from a Zeeman slowed atomic beam and then loaded into the optical dipole trap where they are evaporatively cooled to quantum degeneracy. Our simplified system offers a high degree of flexibility in trapping geometry for studying ultracold Fermi and Bose gases.

Evaporative Cooling of Atoms to Quantum Degeneracy in an Optical Dipole Trap

We discuss our experimental results on forced evaporative cooling of cold rubidium 87Rb atoms to quantum degeneracy in an Optical Dipole Trap. The atoms are first trapped and cooled in a magneto-optical trap (MOT) loaded from a continuous beam of cold atoms [1]. More than 1010 atoms are trapped in the MOT and then about 108 atoms are transferred to a Quasi-Electrostatic Trap (QUEST) formed by tightly focused CO2 laser (λ = 10.6μm) beams intersecting at their foci in an orthogonal configuration in the horizontal plane. Before loading the atoms into the dipole trap, the phase-space density of the atomic ensemble was increased making use of sub-doppler cooling at large detuning and the temporal dark MOT technique. In a MOT the phase-space density of the atomic ensemble is six orders of magnitude less than what is required to achieve quantum degeneracy. After transferring atoms into the dipole trap efficiently, phase-space density increases by a factor of 103. Further increase in phase-space density to quantum degeneracy is achieved by forced evaporative cooling of atoms in the dipole trap.The evaporative cooling process involves a gradual reduction of the trap depth by ramping down the trapping laser intensity over a second. The temperature of the cold atomic cloud was measured by time-of-flight (TOF) technique. The spatial distribution of the atoms is measured using absorption imaging. We report results of evaporative cooling in a single beam and in a crossed double-beam dipole traps. Due to the large initial phase space density, and large initial number of atoms trapped, the quantum phase transition occurs after about 600 ms of evaporative cooling in our optimized crossed dipole trap.

Microwave-induced Evaporation in a Crossed Dipole Trap

We present a way of evaporative cooling using microwave-induced transitions in a crossed-beam optical dipole trap. By combining the optical and magnetic forces with gravity it allows to spatially select the most energetic atoms and drive them out of the trap by microwave. After 480 ms of evaporation, our data show the phase space density of the Cs atoms increases by a factor of 3.2 and the temperature is reduced from 2.4μK to 400 nK. The cooling efficiency is mainly limited by the trap heating. This method provides another way to cool neutral atoms in optical trap and reach temperatures in the nano-Kevin regime.

All-optical Bose-Einstein condensation using a compressible crossed dipole trap

We describe an all-optical method of making a $^{87}\mathrm{Rb}$ Bose-Einstein condensate (BEC). Atoms are first cooled in an optical lattice and loaded into a crossed dipole trap with $1.06\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ light. Then the density is increased by dynamically reducing the trap size, while the atoms are evaporatively cooled by reducing the light intensity. Every $3.3\phantom{\rule{0.3em}{0ex}}\mathrm{s}$, we obtain a nearly pure BEC with $3.5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms in their lowest internal energy state.

Evaporative cooling in a crossed dipole trap.

Laser cooled sodium atoms are trapped in an optical dipole force trap formed by the intersection of two 1.06 \ensuremath{\mu}m laser beams. Densities as high as $4\ifmmode\times\else\texttimes\fi{}{10}^{12}$ atoms/c${\mathrm{m}}^{3}$ at a temperature of $\ensuremath{\sim}140$ \ensuremath{\mu}K have been obtained in a $\ensuremath{\sim}900$ \ensuremath{\mu}K deep trap. By reducing the trap depth over a 2 s interval, we have evaporatively cooled the atoms to a final temperature of $\ensuremath{\sim}4$ \ensuremath{\mu}K at a density of $6\ifmmode\times\else\texttimes\fi{}{10}^{11}$ atoms/c${\mathrm{m}}^{3}$. This corresponds to a factor of 28 increase in atomic phase-space density.