Quantum Degenerate Of Fermi-Bose Mixtures Of ⁴⁰K And ⁸⁷Rb

Starting with the observation of Bose-Einstein condensation in single-component bosonic gases and Fermi degeneracy in spin-polarized Fermi gases,the field of ultra-cold quantum gases is rapidly expanding to studies of mixed systems of different atomic species with different statistics, different trapping properties,masses and interaction.The studies of the mixed systems open up the new avenue for the many-body physics,long-range interacting systems,strongly correlated phases and quantum simulation. Especially,when the means of strong,periodic confinement as demonstrated in experiments with optical lattices and the strong resonant interactions which can be produced by Feshbach resonances are applied into this regime,the researches of the Bose-Fermi mixed gases show the beautiful perspective.The goal of our work is to establish the experimental apparatus for ⁸⁷Rb BEC and ⁴⁰K DFG and perform the associated scientific researches.The contribution of this thesis is doing a series of work to realize the quantum degeneracy of ⁴⁰K and ⁸⁷Rb,based on the established double-MOT cooling experimental setup,and achieving the BEC of ⁸⁷Rb and the DFG of ⁴⁰K.This is the first time to achieve the DFG at home.The experimental protocol:the double-MOT structure is adopted by our lab and the mixtures of ⁴⁰K and ⁸⁷Rb are selected as the workhorse.Firstly,fermionic ⁴⁰K and bosonic ⁸⁷Rb atoms is simultaneously magneto-optical trapped in collection cell,and then the precooled atoms is pushed into the science cell in which the MOT is performed again.Finally,the cold atoms are loaded into the QUIC trap and the evaporative cooling is performed.Through the above process,the BEC of ⁸⁷Rb can be achieved,and the DFG of ⁴⁰K can also be realized by sympathetic cooling with the evaporated Rb.The thesis mainly includes the following parts:1,some improvement has been made about the semiconductor laser system used in the experiment.Firstly,the injection configuration is changed from the three beams of ⁸⁷Rb cooling,⁴⁰K cooling and repumping injected into TA1(TA:Tapered amplifier) and TA2 respectively to ⁸⁷Rb cooling light injected into TA1 and ⁴⁰K cooling coupled with ⁴⁰K repumping light injected into TA2,to avoid the instability of the output power;Secondly,the pinhole possessing the coupling efficiency 90%is used for the filter of the beam mode instead of the optical fiber possessing the coupling efficiency 60%,this method increases the power for cooling atoms and polarization-maintaining problem do not exist.Thirdly,the transport efficiency from MOT1 to MOT2 is improved through the way of pulse-loading,and the required beams in the experiment including the probe beam,the pump beam,and repumping beam are set up.Finally,the detection system of absorption image is established.2,Designing and making all kinds of circuits required for the experiment.The exact experimental sequence is needed in the experiment and the realization of the sequence needs many circuits containing the opto-coupler circuits,driver circuits for the mechanical shutter,and the switch circuits for the current etc.These circuits are self-made and used to the control of the optical field and magnetic field.3,The BEC of ⁸⁷Rb and the DFG of ⁴⁰K are achieved in the experiment. After the magneto-optical trapping of the two species of atoms,the process of compressed MOT,molasses,and optical pump is performed,and then the cold atoms is compressed in the quadrupole magnetic trap and transferred into the QUIC trap.Through the evaporation cooling in the QUIC trap,the quantum degeneracy of Bose-Fermi mixed gases is achieved.The density distributions gained from the absorption images are theoretically analyzed and the experimental date is fitted.The critical temperature for BEC is about 500nK with the atom number 10⁵,and the quantum behavior in the case of ⁴⁰K is also analyzed.4,We study ⁸⁷Rb BEC loading into the pulse of the one-dimensional optical lattice experimentally,in which the lattice is turn on abruptly,held constant for a variable time and then turn off abruptly.The measurement of the depth of the optical lattice is obtained by Kapitza-Dirac scattering.The temporal matter-wave-dispersion Talbot effect with Rubidium BEC is observed by applying a pair of pulsed standing wave(as phase gratings) with the separation of a variable delay.