High Efficiency Magnetic Transport Of Ultra-Cold Atoms And The Research Of Raman Coupling In Cold Atoms With Optical Phase-Locked Loop System

To create ultracold quantum gases and to perform experiments with Bose-Einstein condensates, there are several technical requirements to be met. Optical and magnetic forces are used to capture 87Rb atoms at a temperature of 300 K and cool them over nine orders of magnitude to below 300 nK while storing them in a trap. This requires laser light at different well defined frequencies as well as properly designed magnetic fields. At all stages of the experiment the atoms need to be protected from collisions with background gas atoms, which demands ultrahigh vacuum (UHV) conditions.Producing ultracold quantum gases of alkali atoms involves laser cooling and usually the first cooling stage is realized by a magneto-optical trap (MOT). Operating a MOT involves laser beams from six directions. Together with an imaging system, ports for a vacuum pump and the atom source they consume quite some space. This restricts the optical access to the trapped atoms when it comes to set up tools for performing experiments with the atomic sample. To circumvent these restrictions, one can move the atoms to another position after trapping and pre-cooling them in the MOT. A spatial separation also helps to solve another task, which consists in providing enough atoms when the MOT is loaded while ensuring low pressure and long trap lifetimes at the later stages of the experiment. Implementing a differential pumping stage between the MOT and the separated experimental region allows to obtain the required pressure difference. In our new setup 87Rb atoms are loaded into the MOT in a special vacuum chamber and are then transferred magnetically to a glass cell at a pressure below 10-9 Pa. During the transport we move the atoms over a distance of 49.8 cm and around a corner of 60°. In the glass cell the atom cloud is magnetically trapped and evaporatively cooled to form a BEC. The spatial separation between MOT and final trap position allows excellent optical access to perform a multitude of experiments.Experiments on coherent interaction of light with matter require the involved laser fields to be coherently coupled. This implies that their phase and frequency difference has to be stabilized to a high degree. The most versatile method for the preparation of coherent light fields is that of optical phase locking. An optical phase locked loop stabilizes the phase and frequency of a slave laser so that its phase follows that of a second master laser. The pioneering work on optical phase locked loops has been done in the 1960’s, and they have become a well established tool to obtain phase coherent lasers, not only for the generation of coherently prepared media, but also for coherent optical communication systems, precision spectroscopy and high accurate frequency stabilization of lasers.Spin-orbit coupling (SOC) and Zeeman fields are crucial ingredients for many topological quantum matters. The recent experimental realization of synthetic SOC, one-dimensional (1D). Though significant experimental progresses have been made, a bottleneck in current studies is the lack of a two-dimensional (2D) synthetic SOC, which is crucial for realizing high-dimensional topological matters. Here, we report the experimental realization of 2D SOC in ultracold 40K Fermi gases using three lasers, each of which dresses one atomic hyperfine spin state. Through spin injection radio-frequency (rf) spectroscopy, we probe the spin-resolved energy dispersions of dressed atoms, and observe a highly controllable Dirac point created by the 2D SOC. Our work paves the way for exploring high-dimensional topolog-ical matters in ultracold atoms using Raman schemes. However, in 2D SOC (e.g., Rashba type), a perpendicular Zeeman field, which opens a band gap at the Dirac point and induces topological properties, has not been realized in experiments for ultracold atoms. Here we propose and realize a simple scheme for generating 2D SOC and a perpendicular Zeeman field simultaneously in ultracold Fermi gases by tuning the polarization of three Raman lasers that couple three hyperfine ground states of atoms. The resulting band gap opening at the Dirac point is probed using spin injection radio-frequency spectroscopy. Our observation may pave the way for exploring topological transport and topological superfluids with exotic Majorana and Weyl fermion excitations in ultracold atoms.