Study Of Bose-Fermi Superfluid Mixture And Quantum Communication Via Freespace Channel

The study of superfluidity based on ultracold atoms is the important direction in the research of ultracold quantum gas.In this thesis,we first introduced the experiment system and procedures for the generation of 6Li and 41K Bose-Fermi superfluid mixture.To achieve the Bose-Fermi superfluid mixture,we built a complex experiment ap-paratus,which included an ultrahigh vacuum system,resonance laser system,laser fre-quency and intensity controlling system,magnetic system,procedure controlling sys-tem,water cooling system,Radio Frequency(RF)system,and state monitor system.Experiment began in the laser cooling phase of the two species,which included a Zee-man Slower of 6Li atoms,an advanced 2D+ MOT for 41K atoms,a 3D MOT and a Compressed MOT for both species,a UV MOT for 6Li atoms,and a gray molasses for 41K atoms.After laser cooling phase,the atom clouds were transported to the sci-ence chamber by a magnetic transport apparatus.After magnetic transport phase,we performed the RF driven evaporative cooling for 41K atoms in the optically plugged magnetic trap.By driving the transition of |2,2>? |1,1>,we expelled 41K atoms with high energy out of the trap,and ketp the cooler atom cloud.During the evapora-tive cooling of 41K atoms,the 6Li atomic cloud was cooled sympathetically.After the evaporative cooling phase,we transported the atom cloud into a special designed disk-like optical dipole trap system.In the disk-like optical dipole trap,we first performed the state transfer of the two species by RF pulses.During this phase,the 41K atoms were transported into the lowest energy state,while the 6Li atom cloud was produced to be the balance mixture of the two lowest energy states.Then we performed further evaporative cooling by lowing the trap depth.Eventually,we obtained a BEC of 41K atoms with atom number of 1.8 x 105(condensation fraction>80%)and BCS super-fluid of 6Li atoms with atom number of 1.5 x 106(T/TF<8%).During the RF drive evaporative cooling phase,we also achieved degenerate mixture of the two species by carefully controlling the evaporation procedure.In the superfluid mixture of 41K and 6Li atoms,we noticed that there was a defect in the distribution of 6Li atoms where 41K atoms existed.This indicated the interaction between the two superfluid and could be explained by mean field interaction.Also we nucleated vortex lattices in both superfluids by stirring the superfluids mixture with two blue-detuning laser beams.After the production of vortex lattices,we measured the vortex number at different experiment conditions.By comparing the vortex number difference between that in different supefluids,we also observed the interaction of the two superfluid.This thesis also introduced the experimental study of quantum communication via freespace channel.The result of entanglement distribution experiment showed the vio-lation of Bell inequality over 100km,while the result of teleportation showed the quan-tum state could be transported over 97 km.Also there is a brief introduction of the fibers polarization controlling system for the entanglement source in the quantum satellite.