The Achievement Of ⁸⁷Rb Bose-Einstein Condensation And The Laser Cooling Of ⁶Li And ⁴⁰K

The achievement of Bose-Einstein Condensation and Fermi Degeneracy is a grand progress not only in the atom and molecular physics, but also a great milestone in the history of physics. People get a macroscopic and controllable quantum platform and the achievement bring great confidence of controlling the quantum world to people. Now the research of the Bose- Fermi Mixtures(BFM) draw much attraction of scientists, because the BFM present a new testbed for many important physics problems such as the high-Tc superconductivity, the strong interaction quatum systems, the production of ultracold molecules and the investigation of BEC-BCS crossover regime. The prerequisition of these research topics is the quantum degenerate of the Bose-Fermi mixtures.Our work focuses on the experimental achievement of the BFM. In our experiment, we use one bosonic species 87Rb and two femionic species 6Li,40K. Now we have successfully trapped 87Rb,6Li and 40K atoms in magneto-optical trap and realized the 87Rb Bose-Einstein Condensation. We adopted the double-MOT scheme. The first step is magneto-optical trapping of 7Rb atoms in a low vacuum stainless-steel chamber. The second step is pushing the atoms into a high vacuum quartz glass cell with a pushing beam and trapping the atoms again with the magneto-optical trap. The third step is loading the atoms into a plugged quadrupole magnetic trap. The forth step is achieving BEC by evaporative cooling the atoms. We constructed the plugged quadrupole magnetic trap with 532nm solid state laser source and 767nm semiconductor laser source respectively, and get the BEC independently. We also gave a proposal for constructing a three dimensional isotropic optical trap. Now the trap is under construction.The thesis mainly includes four parts:1.We have constructed a experimental platform for the the quantum degenerate BFM and successfully trapped the 87Rb,40K and 6Li atoms in magneto-optical trap. We captured 87Rb and 40K atoms directly from the background vapor in the low vacuum chamber. The 6Li atoms emitted from the heated source was precooled by 2D-MOT firstly and pushed to the low vacuum chamber with a near-resonant beam, where they were stably trapped in MOTA. At last, the atom number of the 87Rb,40K and 6Li in MOTA was 1.5×109,4.0×108 and 4.0×108, respectively.2. We successfully obtained the Rb Bose-Einstein condensate in quadrupole trap optically plugged with a 532nm laser beam. Firstlly, we transferred the atoms to the high vacuum cell and cooled the atoms to a temperature of 129μK which broke the Doppler cooling limit with a technique which we denoted as decompressed magneto-optical trap. Then we loaded the atoms into a magnetic trap with a efficiency of 25%.3. We also successfully got the 87Rb Bose-Einstein condensate in a quadrupole trap optically plugged with a 767nm laser beam。 The advantage of using 767nm laser as the plug is the lower required power and more precise and flexible control over the beam properties and time sequences. Moreover, the beam quality passed through AOM remains nice. The signal-noise ratio (SNR) of the experiment result is better than the former.4. We gave a proposal for constructing a three dimensional isotropic optical trap. We will use three common Gaussian far red detuned laser beams which are orthogonally intersecting in the vacuum cell and eliminate the effect of gravity with the help of a pair of quadrupole coils. Finally, we give an experimental scheme in detail. The relevant experiment is under construction.