Simple method for generating Bose-Einstein condensates in a weak hybrid trap

Abstract

We report on a simple novel trapping scheme for the generation of Bose-Einstein condensates of 87 Rb atoms. This scheme employs a near-infrared single beam optical dipole trap combined with a weak magnetic quadrupole field as used for magneto-optical trapping to enhance the confinement in axial direction. Efficient forced evaporative cooling to the phase transition is achieved in this weak hybrid trap via reduction of the laser intensity of the optical dipole trap at constant magnetic field gradient.A simple and robust method for the generation of quantum degenerate atomic gases with decent particle number and repetition rate is of interest for the study of their fundamental properties [1][2][3] or their applications in atomic inertial sensors [4] and gravimeters [5], as well as in microgravity [6]. Here, we describe a very simple method for the generation of a Bose-Einstein condensate (BEC) in a single beam near-infrared optical dipole trap (ODT). Optical dipole traps offer great potential with respect to the criteria mentioned above. Forced evaporative cooling in such traps is usually achieved by reducing the power of the ODT laser beam [7] and rethermalization times are generally short due to the high trapping frequencies in the kHz-regime usually provided by an ODT. However, power reduction also reduces the confinement of the atoms in the trap which in turn negatively affects trap frequencies, peak atomic density, elastic collision rate, and as a consequence the efficiency of forced evaporation. This counteracts the gain in phase space density by the cooling of the atomic cloud, thus preventing the regime of run-away evaporation in an ODT with this simple method [8]. Quantum degeneracy can nonetheless be reached in these traps, provided the initial atomic and phase space densities were high enough [9,10]. Nevertheless, the necessary compromise between high initial densities and high initial trapping volume severely affects the maximum number of particles in the BEC and additional sophisticated concepts for reaching optimized initial atomic and phase space densities may be required [11].The most simple realization of an ODT is to focus one single far-off resonant high power laser beam onto the atomic ensemble. However, due to the rather low confinement of the atoms in the axial direction of these single beam ODTs, the high initial atomic and phase space densities needed to reach quantum degeneracy are very hard to realize. This is particularly the case for single beam ODTs formed from a near-infrared laser source [12]. In * Rasel@iqo.uni-hannover.de contrast, the wavelength of a CO 2 laser of ∼ 10.6 µm provides an axial trapping frequency an order of magnitude higher compared to an ODT formed from e.g. a Nd:YAG laser at a wavelength of 1064 nm. This stronger confinement is still enough to allow for the realization of a BEC with more than 10 5 atoms [13]. Nevertheless, this method is bound to the use of far-infrared laser wavelengths with all the associated technical implications. If the use of laser wavelength...

Efficient production of an 87Rb F = 2, mF = 2 Bose-Einstein condensate in a hybrid trap

“…Therefore in the hybrid trap it is much easier to obtain a BEC than in a pure single beam ODT, even for a weak gradient [25].…”

Quantum Test of the Universality of Free Fall

“…As shown in Fig. 2 the contrast of the resulting interference patterns is presently at the few percent level and can be further enhanced by additional cooling and state selection and by employing a dipole trap common to both species [38]. The Eötvös ratio η Rb,K can then be calculated from the obtained single-species signals using Eq.…”

Testing the universality of free fall with rubidium and ytterbium in a very large baseline atom interferometer

“…Abund mW. The Bose-Einstein condensation in a single beam dipole trap at this wavelength for 87 Rb was already shown in a weak hybrid trap configuration in [49]. Therefore, a 1960-nm trap appears to be an ideal solution, and lasers with output powers up to 100 W are available.…”