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arXiv:0711.2598 · Journal of Physics B Atomic Molecular and Optical Physics

Magnetic trapping of a cold Rb–Cs atomic mixture

Margaret Harris, Patrick Tierney, Simon L. Cornish

Published Jan 22, 2008• 25 citations
arXivHTMLPDF

Abstract

We present an apparatus for the study of an ultracold gaseous atomic mixture of 133Cs and 87Rb. The mixture is prepared using a double magneto-optical trap (MOT) system in which a two-species pyramid MOT acts as a source of cold atoms for a `science' MOT. Measurements of the interspecies trap loss rate coefficients beta_RbCs and beta_CsRb in the science MOT are reported. After the initial MOT phase, atoms in the mixture are optically pumped into the magnetically trappable |F=3,m_F=-3> and |F=1,m_F=-1> states of Cs and Rb (respectively) and loaded into an Ioffe-Pritchard magnetic trap. We demonstrate a novel technique for limiting the interspecies loss rate in the science MOT by spatially separating the two trapped atom clouds, which greatly enhances the number of atoms which can be loaded into the magnetic trap.

DOI
10.1088/0953-4075/41/3/035303

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We present an apparatus for the study of an ultracold gaseous atomic mixture of 133Cs and 87Rb. The mixture is prepared using a double magneto-optical trap (MOT) system in which a two-species pyramid MOT acts as a source of cold atoms for a `science' MOT. Measurements of the interspecies trap loss rate coefficients beta_RbCs and beta_CsRb in the science MOT are reported. After the initial MOT phase, atoms in the mixture are optically pumped into the magnetically trappable |F=3,m_F=-3> and |F=1,m_F=-1> states of Cs and Rb (respectively) and loaded into an Ioffe-Pritchard magnetic trap. We demonstrate a novel technique for limiting the interspecies loss rate in the science MOT by spatially separating the two trapped atom clouds, which greatly enhances the number of atoms which can be loaded into the magnetic trap.
This thesis reports on the realisation and characterisation of a magnetically trapped ultracold atomic mixture of 87Rb and 133Cs in the F = 1, mF = −1 and F = 3, mF = −3 hyperfine states respectively. A compact two-species double magneto-optical trapping (MOT) apparatus is constructed in which a pyramid MOT acts to provide an independent flux of both atomic species for capture in the ultra-high vacuum science region of the apparatus. For the two-species science MOT in which this atom flux is captured, interspecies light assisted inelastic collisions are found to be a highly significant loss mechanism. A novel optical pressure spatial displacement technique is developed to minimise such losses, allowing near independent simultaneous loading of up to ' 8 × 108 87Rb and ' 3 × 108 133Cs atoms into an Ioffe-Pritchard ‘baseball ’ magnetic trap at magnetic bias fields of 166.70(6) and 165.50(6) G respectively. At the loaded 87Rb and 133Cs atom number densities of 1.78(6) × 109 and
This thesis describes a new apparatus designed to study cold, ultracold, and quantum degenerate mixtures of rubidium and caesium atoms. The Rb- Cs mixture is prepared using a double magneto-optical trap (MOT) system in which a two-species pyramid MOT acts as a source of cold atoms for a 'science' MOT. The first results of experiments on the magneto-optically trapped mixture are presented, including measurements of trap loss rates due to single-species and interspecies inelastic collisions. A technique for reducing interspecies loss by spatially separating the MOTs during loading is described. This technique allows 50-50 mixtures of Rb and Cs atoms to be loaded into a magnetic trap at close to their respective maximum single- species atom numbers. Alternatively, one species can be loaded with arbitrarily small amounts of the other. The displaced MOT technique is thus аn excellent starting point for investigations of interspecies Feshbach resonances and sympathetic cooling of Rb-Cs mixtures in magnetic and optical traps. In addition, a model of polarisation spectroscopy based on numerical integration of population rate equations is described. Theoretical polarisation spectra generated by the model are shown to agree with experimental spectra for the F = I + 1/2 → F' transitions in Rb and Cs. An investigation of the sub-Doppler dichroic atomic vapour laser locking (DAVLL) technique demonstrates how locking signals can be optimised for the Rb D2 transitions. The role of polarisation purity in generating the spectra is discussed, and impurities are modeled using a Jones matrix approach. Comparisons with polarisation spectroscopy and DAVLL are used to enhance understanding of atom-light interactions in spectroscopic systems, and indicate methods for optimising locking signals for use in cold atom experiments.
We present the simultaneous trapping and cooling of 85{}^{85}85Rb, 87{}^{87}87Rb and 133{}^{133}133Cs in a triple-species magneto-optical trap (MOT). This demonstration is obtained using an all-fibre compact and robust laser system based on telecom 1.5 μμμm and 2 μμμm technologies. We characterise the two-body interspecies losses in the double and triple-species MOT. We calculate the two-body interspecies trap-loss coefficient for the 85{}^{85}85Rb/133{}^{133}133Cs and the 87{}^{87}87Rb/133{}^{133}133Cs pairs, representing a variation of less than 7 \% in atom number. No losses are observed between 85{}^{85}85Rb and 87{}^{87}87Rb in our experimental conditions. We find that interspecies interactions inside the triple-species MOT do not prevent trapping and cooling 108^{8}8 atoms for each species, making our system suitable for future multi-species cold-atom interferometry applications.
We experimentally demonstrate a novel scheme to simultaneously confine two atomic species of (87)Rb and (133)Cs with adjustable spatial separation by a controllable double-well magneto-optic trap. Using a single-loop wire and a magnetic bias field, the two clouds, each containing more than 1 x 10(6) atoms, are spatially separated above and below the wire center of the double-well MOT. The cloud interdistance can be controlled by independently varying the wire current and external bias field. This allows to load the double-well magnetic trap, and to study the dynamics of cold collisions between two-species atoms.
We describe a three-dimensional (3D) magneto-optical trap (MOT) capable of simultaneously capturing 85Rb and 133Cs atoms. Unlike conventional setups, our system utilizes two separate laser systems that are combined before entering the vacuum chamber, enabling the simultaneous trapping of two different atomic species. Additionally, in our 3D MOT configuration, two (of three) pairs of laser beams are not orthogonal to the chamber surfaces but are aligned at a 45° angle. With a total trapping laser power of 8 mW and repump laser power of 4 mW for Rb atoms, and a total trapping laser power of 7.5 mW and repump laser power of 1.5 mW for Cs atoms, we achieve optical depths (OD) of 3.71 for Rb and 3.45 for Cs, demonstrating efficient trapping for both species. Our 3D MOT setup allows full horizontal optical access to the trapped atomic ensembles without spatial interference from the trapping or repump laser beams. Moreover, the red detuning for trapping both atomic species is smaller than in traditional configurations. This system offers a versatile platform for exploring complex phenomena in ultracold atom physics, such as Rydberg molecule formation and interspecies interactions.
In this article, we report the measurement of collision-induced loss rate coefficients β_{Li,Rb} and β_{Rb,Li}, and also discuss means to significantly suppress such collision induced losses. We first describe our dual-species magneto-optical trap (MOT) that allows us to simultaneously trap > 5x10^8 7Li atoms loaded from a Zeeman slower and > 2x10^8 85Rb atoms loaded from a dispenser. We observe strong interspecies collision-induced losses in the MOTs which dramatically reduce the maximum atom number achievable in the MOTs. We measure the trap loss rate coefficients β_{Li,Rb} and β_{Rb,Li}, and, from a study of their dependence on the MOT parameters, determine the cause for the losses observed. Our results provide valuable insights into ultracold collisions between 7Li and 85Rb, guide our efforts to suppress collision induced losses, and also pave the way for the production of ultracold 7Li85Rb molecules.