Experimental Research Of Superradiance Lattice In ⁸⁷Rb Bose-Einstein Condensates

Ultracold atomic gases is a unique system with great research value and vast applications.A new experimental system has been built in our laboratory.The rapid production of high-quality ⁸⁷Rb Bose Einstein condensates has now been achieved,and research on one-dimensional superradiance lattice has been developed,in which backward directional scattering can be observed.Firstly,this article introduces the construction of the experimental system.Vacuum system with ultrahigh vacuum degree is the basis of ultracold atom experiment.The vacuum system's structure and process of air exhaust are introduced in chapter 3.Cooling and trapping of atomic gases requires the combination of various structures of light beams and magnetic field.In chapter 3,the stabilization of semicondunctor laser by saturated absorption spectroscopy,fast switching,frequency shifting,power adjustment and feedback control of light beams are introduced.In one experiment process,the light beams,magnetic field,radio frequency radiation,and microwave radiation are required to be switched or remotely adjusted by turns.This has been done by the main controlling computer through the electronic circuit.The basic process of producing BEC is:2D MOT collects the atoms to form an atomic beam through which atoms are transferred to the 3D MOT region;3D MOT cools and captures atomic gas and then adiabatically load it into the magnetic trap;RF evaporative cooling is performed to cool the atoms further in magnetic trap;precooled atomic gas in magnetic trap is transferred to the optical dipole trap,where BEC finally emerges by another evaporative cooling.Chapter 3 explains each of these steps in detail.Chapter 4 and 5 introduce our research on one-dimensional superradiance lattices.Superradiance is a collective spontaneous emission of oscillating dipoles,and the spontaneous emission rate of atoms in superradiance state is greater than the spontaneous emission rate of single atoms.Superradiance emission is a kind of directional radiation.The study of superradiance is of great significance.Superradiance state excited by a resonance light is expected to observe the collective Lamb shift.Our research focuses on the transfer of superradiance states by two coherent coupling light beams.The directional radiation can be changed to other directions.Superradiance states dressed by the coupling beams form a tightly bound lattice in momentum space,which is called superradiance lattice.With an optical phase-lock loop?OPL?,the probe laser and coupling laser can be locked together.By changing the OPL's parameter,the probe laser's frequency can be scanned while keeping the coupling laser locked.In Chapter 5,the related theory background and experimental observation of backward directional scattering in one-dimensional superradiance lattice are reported.