Production of Rubidium Bose—Einstein Condensate in an Optically Plugged Magnetic Quadrupole Trap

Abstract

We have experimentally produced rubidium Bose-Einstein condensate in an optically-plugged magnetic quadrupole (OPQ) trap. A far blue-detuned focused laser beam with a wavelength of 532 nm is plugged in the center of the magnetic quadrupole trap to increase the number of trapped atoms and suppress the heating. A radio frequency (RF) evaporative cooling in the magneto-optical hybrid trap is applied to decrease the atom temperature into degeneracy. The atom number of the condensate is 1.2(0.4)×105 and the temperature is below 100 nK. We have also studied characteristic behaviors of the condensate, such as phase space density (PSD), condensate fraction and anisotropic expansion.PACS numbers: 67.10.Ba; 64.70.fm; 37.10.De Since the experimental observation of Bose-Einstein condensate (BEC) in a dilute gas [1][2][3], the ultracold quantum gas has become a reachable tabletop to carry on a wide range of research, such as accurate measurement on physical constants [4,5] [19,20], and magneto-optical combination trap [21]. Compared to many other kinds of traps, the optically-plugged magnetic quadrupole (OPQ) trap has many advantages, which has been demonstrated in some groups [3,[22][23][24][25]. First, the tight confinement allows for fast radio frequency (RF) evaporative cooling and the large trapping volume offered by the magnetic quadrupole trap facilitates loading of a large number of atoms from the magneto-optical trap (MOT). Secondly, the atom cloud is positioned exactly in the center of the glass cell on the symmetry axis of the quadrupole coil pair, which ensures very good optical access to atoms. Third, the quadrupole coil pair allows to create large homogeneous magnetic fields by switching to copropagating currents, which we can use to address Feshbach resonances.In this paper, we produce rubidium BEC in an OPQ trap. Here we show that the laser beam with a wavelength of 532 nm can be used to efficiently obtain 87 Rb BEC despite the large detuning of the optical plug laser * Electronic address: kjjiang@wipm.ac.cn from the rubidium transition line at 780 nm. The atom number of the condensate is 1.2(0.4) × 10 5 and the temperature is less than 100 nK, which matches the basic requirements for further advanced studies. We have also studied characteristic behaviors of the condensate, such as phase space density (PSD), condensate fraction and anisotropic expansion. In the near future we will use the obtained rubidium BEC to study the collective oscillations of the quantum gas, and generate an ultracold Bose-Femi mixture using the sympathetic cooling in the same experimental setup where we have cooled fermionic atoms like 6 Li and 40 K [26,27].We use the two-MOTs configuration to realize 87 Rb BEC. The optical arrangement is shown in Fig.1. Two diode lasers (DLs) are individually frequency locked on the two crossover transitions |F = 1 → |F ′ = 1, 2 and |F = 2 → |F ′ = 2, 3 , respectively, using the standard saturation absorption spectroscopy (SAS) method. DL2 affords cooling, probing and pushing beams, after passing...

Optimizing the optical imaging system by \emph{in-situ} imaging the plugged hole in the ultracold atoms

“…1. The detuning and power of the plug beam are both much smaller than those in reference [28], which greatly improves the experimental stability and simplicity. The hole position exactly overlaps the the zero point of the magnetic field, suppressing the spin-flip loss by pushing atoms away from approaching the hole.…”

“…Rubidium BEC can be produced in an optically plugged magnetic quadrupole trap (OPQT) as described in our previous work [28]. Here we focus on how to optimize the optical imaging system using the plugged hole as a imaging reference.…”

Expansion dynamics of a spherical Bose–Einstein condensate*

“…The experimental configuration is composed of double magneto-optical traps (MOTs), which is similar to our previous works [31,32]. 87 Rb atoms are cooled and trapped in the first MOT and then transferred to the second MOT with a series of optical pushing pulses.…”

Observation of phonon parametric down-conversion in a spherical Bose-Einstein condensate

“…1(a), which is developed from the Ref. [21]. The spherical trap is composed of the optical dipole trap and the gravity.…”