Experimental Study Of Gravity's Influence On Loading Cold Atoms Into Magnetic Trap

Ultracold atoms system has significant advantages such as highly controlled degrees of freedom.For example,we can accuracy control the number of atoms,the temperature of system,components of different spin,the structure of bound potential and the interaction between atoms.In recent years,ultracold atoms system becomes ideal quantum simulation platform cause its rapid development.It provides an effective platform for the research such as Quantum Hall Effect,Magnetic monopoles,and Superfluid.Since 2012 our laboratory reported the spin orbit coupling of quantum degenerate Fermi gases for the first time,in 2013 our laboratory began to build a new 87Rb-40K experiment platform,aims to achieve Bose Einstein Condensation(BEC)and Degenerate Quantum Fermi gas(DFG),after then research frontier in the field of related areas of ultracold atoms.This paper introduces the new experimental system,the cooling technology,as well as the influences of gravity on 87Rb atoms recaptured by the quadrupole magnetic trap after Sisyphus cooling.We choose the suitable magnetic trap on the basis of theoretical analysis to improve atoms' capture efficiency.In the vacuum system,we use laser cooling technology,magnetic trap,optical trap,magneto optical trap technique to obtain samples of cold atoms,and then the atoms could be further cooled by evaporative cooling.The evaporative cooling process needs enough elastic collision which can't happen in 40K Fermi gas at ultra-low temperature.We use Synchronous cooling technology by mixing the 40K Fermi gas and 87Rb Bose gas,through the elastic collision between them to cooling 40K and achieve its quantum degeneracy.We design a 2D-3D magneto optical trap through the constant improvement and optimization,the final system through multiple reflections of the light beam improved utilization of beam and increase the volume of magneto optical trap.Quadrupole magnetic trap is the simplest magnetic trap which can capture atoms.When the quadrupole magnetic field coils are placed vertical and horizontal respectively,the gravity's effect is investigated on recapturing atoms with the magnetic quadrupole trap.We observe the oscillation of 87Rb atoms in the quadrupole magnetic trap by time-of-flight and absorption image.The magnetic field distribution in both cases is calculated and presents that 87Rb atoms' oscillation comes from the offset of center of the magnetic field due to gravity.After calculating and analyzing the magnetic field gradient B' to balance the gravity for state of 87Rb atom,we explore 87Rb atoms oscillation,and choose the configuration with placing the magnetic field coils horizontally to increase the recapture efficiency of quadrupole magnetic trap.We choose 532nm optical plugged magnetic field to avoid the loss of atoms' number caused by Majorana Spin Flipping.For now,we get a large number of both 87Rb and 40K atoms with high density in the optical plugged magnetic field.The gases would then be transferred to a crossed far red detuning optical dipole trap.There,the gases could be further cooled to a quantum degenerated state.87Rb atoms'Bose Einstein Condensation is observed on January 28,2016 at the first time at our new 87Rb-40K experiment platform.