Design And Realization Of Magnetic Trap In Cold Atom Experiment

In cold atom experiment,no matter trapping atoms in initial experiment stage,evaporation afterwards or all kinds of manipulations in the final stage,it needs a stable trap to load the atoms.In every experimental stage,constructing trap has a direct influence on experimental result.Different experiments call for different sorts of traps,from simplest quadrupole trap to optimized QUIC trap,Ioffe-Pritchard trap,as well as some special structure trap constructed by experimenters.Furthermore,some international groups devote to minimize the trap,in a micrometer circuit board they print very thin circuits,skillfully combine magnetic field created by different currents to form micro trap,trapping atoms.The traps talked above are constructed by magnetic field,using the character of atomic magnetic moment,the other optical trap uses far detuned laser,inducing electric dipole moment in atoms,its appearance promotes the flexibility of cold atom experiment greatly,allowing experimenters to choose magnetic field or laser to construct trap.For example,precisely measuring weak magnetic field like earth magnetic field using atom,we choose optical trap to reduce outer magnetic field interference effectively.The development of trap makes a big progress in research and application of neutral atoms,so it is very meaningful to investigate designing and realizing of trap.This thesis firstly looks back to the development of cold atom experiment,introduces the principle of trapping atoms with magnetic optical trap and theory of atomic magnetic Feshbach resonance in the initial cold atom experiment stage.Then theoretically analyze the principle of constructing optical dipole trap using far detuned laser and give rise to calculation method and experimental parameters combining experiment,such as waist,laser power,trap depth and trapping frequency.In the following,theoretically analyze the designing principle of optical lattice,give rise to calculation method of trap depth and trapping frequency,figure out how to choose the frequency and polarization of three beams when constructing three-dimensional optical lattice,preparing for future optical lattice experiment.At last,we introduce the principle of two-dimensional magnetic optical trap designed by us.Our design makes the apparatus compact,accelerate the atom loading rate and now it is among the main stream design in the world.Then this thesis mainly investigates the stability of three dimensional magnetic optical trap and Feshbach resonance coils made by hollowed copper wire.In experiment,we firstly modulate our designed magnetic field with Mathematica,and calculate geometry of coil.Then precisely measure magnetic field created by this pair of round coils in anti-Helmholtz and Helmholtz configuration using magnetic field meter.Compare experimental data and numerical modulation to determine the optimal coil distance,this value plays a key factor for constructing magnetic field,since atom is sensitive to magnetic field,fluctuation of magnetic field will heat atoms.Next step,we calculate necessary cooling water pressure and speed when cooling coils to room temperature and design cooling apparatus.In the following,we give rise to a more accurate method to measure the stability of magnetic field,Rabi flipping and radio frequency spectroscope.We design a mixed trap using quadrupole trap and green laser,making our apparatus more compact and leaving room for further optical lattice experiment.Finally we design a series of magnetic trap to construct magnetic transfer chain,use twelve pairs of coils overlapping half one by one to transfer atoms in a long distance.We analyze the principle and sequence of magnetic transfer procedure and design current drive,computer control and feedback of transfer coils.