Atoms in Optical Lattices: Cooling, Trapping and Squeezing Atoms with Light

Laurent Sanchez-Palencia, G. Grynberg

C. Abou-Jaoudeh

In this thesis, a transportable setup of an Yb atomic source for a lattice optical clock is built and characterized. All three laser setups for cooling and trapping the Yb atoms, together with the vacuum system, are contained on a transportable optical table. The preparation of the atomic sample before doing spectroscopy on the clock transition starts by slowing the atoms in the Zeeman slower. This is followed by trapping the atoms in the pre-cooling and the post-cooling MOTs, before loading the atoms into the optical lattice. Slowing and pre-cooling the atoms is done using the strong transition at 399 nm. This cools the atoms down to around a mK. To successfully load the atoms in the optical lattice, we have to cool the atoms further to beyond 50 μK. This is done by exciting the weak transition at 556 nm. The atoms that are transferred into the post-cooling stage are cooled down to a few tens of μK. The atoms are then ready to be loaded into the optical lattice at the magic wavelength. The amplified laser light at 760 nm inside the 1-D intra-vacuum cavity results in a lattice trapping potential of approximately 50 μK. A transfer efficiency, from the MOT into the optical lattice, of more than 25% was measured. The spectroscopy on the clock transition was done for 171Yb. A step-by-step mechanism was adopted, starting by exciting the forbidden transition at 578 nm inside the post-cooling stage MOT, by using the ”chopped-MOT” method. The 300 kHz Doppler-broadened line is then narrowed down to 3 kHz by switching on the light at 760 nm, while keeping the MOT on. The so-called ”chopped-lattice” technique helped suppress the Doppler-broadening; however the other effects due to the light and the magnetic fields of the MOT were still present. By switching off the MOT’s light and magnetic fields, the Yb atoms are completely trapped in the optical lattice. As a result, the FWHM of the spectroscopy line was reduced by a factor of 10.

S. Lukman Winoto, Marshall T. DePue, Nathan E. Bramall +1 more

We report a way to overcome heating due to the reabsorption of scattered light when relatively many atoms are laser cooled at high density. A sample of $8\ifmmode\times\else\texttimes\fi{}{10}^{7}\mathrm{Cs}$ atoms, with $6\ifmmode\times\else\texttimes\fi{}{10}^{11}{\mathrm{atoms}\mathrm{}\mathrm{cm}}^{\mathrm{\ensuremath{-}}3},$ is loaded into a deep far-detuned one-dimensional optical lattice, which acts as a large volume three-dimensional (3D) trap. Polarization gradient cooling with a separate set of cooling beams is found to work well in this trap, populating the trap's vibrational ground state with more than half the atoms. After cooling, the lattice is shut off adiabatically, leaving a still dense sample at 1.2 \ensuremath{\mu}K. We propose and demonstrate a generalization to a 3D lattice, which will allow many more atoms to be loaded into conservative light traps, and can greatly increase the initial phase-space density for loading magnetic traps.

William D. Phillips

W. Zwerger

David S. Weiss, S. Lukman Winoto, Mark T. Depue

A new method of studying and cooling trapped atoms is discussed, with particular attention to atoms in far detuned, 3D optical lattices. The technique, projection cooling, uses a combination of microwave and optical fields to cycle atoms between hyperfine sublevels. A single vibrational level will remain dark to both the light and the microwaves, so atoms will accumulate there. Cooling below the photon recoil limit is possible with this technique. As a diagnostic tool it promises to yield detailed information about atoms in the lattice, including vibrational spectra and the distribution of atoms among vibrational levels, even in the limit of relatively weak binding to lattice sites. Atoms cooled in this way and then allowed to adiabatically expand in their potentials could reach the Bose-Einstein condensation point in less than a second, or at least get close enough to reach it after only a modest amount of evaporative cooling in a larger volume trap. Atoms so cooled and trapped are also of interest for precision measurements.