In our experiment, we study and intend to manipulate the interaction between the two species viz. rubidium (Rb) and caesium (Cs) at ultracold temperatures. We propose to explore the world of many body physics and small particle physics by inserting a few Cs atoms into a Rb condensate. Our experimental set up consists of a double MOT system, with a magnetic trap in the QUIC configuration. The Rb atoms are cooled evaporatively using a species selective microwave frequency such that Cs remains unaffected due to a 2.4 Ghz difference in their hyperfine transitions, producing a Rb condensate with around 105 atoms.
In our experiment, we study and intend to manipulate the interaction between the two species viz. rubidium (Rb) and caesium (Cs) at ultracold temperatures. We propose to explore the world of many body physics and small particle physics by inserting a few Cs atoms into a Rb condensate. Our experimental set up consists of a double MOT system, with a magnetic trap in the QUIC configuration. The Rb atoms are cooled evaporatively using a species selective microwave frequency such that Cs remains unaffected due to a 2.4 Ghz difference in their hyperfine transitions, producing a Rb condensate with around 105 atoms.
Binary mixtures of ultracold atoms are of great interest in the research field of quantum optics and are studied by several groups aiming at different applications. This paper works with rubidium and caesium, which are simultaneously stored in a magnetic trap. Species-selective microwave cooling is used on the rubidium groundstate hyperfine transition. Caesium is sympathetically cooled via elastic collisions with rubidium. When cooling down the mixture to temperatures below 1 muK, below 4 muK we observe strong losses of caesium. Analysing the dynamics of sympathetic cooling, lower limit for the modulus of the rubidium-caesium triplet s-wave scattering length is estimated.
This thesis reports the formation of a dual-species Bose-Einstein condensate of 87Rb and 133Cs in the same trapping potential. Quantum degenerate mixtures exhibit rich physics inaccessible to single species experiments and provide an ideal starting point for the creation of ultracold dipolar molecules. These molecules offer a wealth of new research avenues including precision metrology, quantum simulation and computation. The experimental method exploits the efficient sympathetic cooling of 133Cs via elastic collisions with 87Rb, initially in a magnetic quadrupole trap and subsequently in a levitated optical trap. Evaporative cooling in the dipole trap must compete against a high interspecies three-body inelastic collision rate \mbox{∼10−25−10−26~cm6/s}. The two condensates each contain up to \mbox{2×104} atoms and exhibit a striking phase separation, revealing the mixture to be immiscible due to strong repulsive interspecies interactions. Sacrificing all the 87Rb during the cooling leads to the creation of single-species 133Cs condensates of up to \mbox{6×104} atoms. In addition this thesis reports the observation of an interspecies Feshbach resonance at 181.7(5)~G and the creation of a pure sample of Cs2 molecules via magneto-association on the 4(g)4 resonance at 19.8~G. These results represent important steps towards the creation of ultracold polar RbCs molecules.
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 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.
We investigate quantum-mechanical interactions between ultracold rubidium and cesium in an optical trap at temperatures of a few microkelvin. Our results provide, on the one hand, an experimental key to understand the collisional properties and, on the other hand, a tool to control the interspecies interactions. By performing loss measurements we locate several Feshbach resonances, which provide insight into the energy structure of weakly bound RbCs molecules near the dissociation threshold and allow for the production of such heteronuclear Feshbach molecules. In the future we will transfer these loosely-bound molecules into the absolute internal ground state. The availability of ultracold heteronuclear ground state molecules will open the door to investigate phenomena associated with ultracold polar quantum gases. In our new experimental set-up we are able to trap and cool rubidium and cesium atoms in their lowest internal states. First we load both species into a two-color magneto-optical trap, having full control over the single-species atom number. We extend the technique of degenerate Raman-sideband cooling to a two-color version, which is able to simultaneously cool and polarize both rubidium and cesium. Thereafter we load the atoms into a levitated crossed optical dipole trap. Because of the presence of the gradient magnetic field the trap is highly state selective and consequently provides perfect spin-polarization of the sample. Furthermore, a coincidence of the magnetic-moment-to-mass ratios of the two species allows for simultaneous levitation of both, which assures an almost perfect spatial overlap between the species. We perform Feshbach spectroscopy in two different spin channels of the mixture within a magnetic field ranging from 20 to 300G. In the lowest spin combination of the species we locate 23 interspecies Feshbach resonances, while in a higher spin mixture we find 2 resonances. The high number of resonances found within this range of magnetic field is unusual for alkali mixtures. The presence of many resonances points to scattering properties of the mixture, which include higher-order coupling mechanisms. The obtained data on the Feshbach spectroscopy provide, on one hand, fundamental experimental input to characterize the Rb-Cs scattering properties and, on the other hand, identification of possible starting points for the association of ultracold heteronuclear RbCs molecules. In addition we show preliminary results on spectroscopy of the binding energy of RbCs dimers, based on a modulation of the magnetic field. The recently obtained Bose-Einstein condensate of Cs atoms, which represents a benchmark for the performance of the present apparatus, will be discussed as well as the potential pathways towards a double-degenerate mixture. We follow two main goals, first the production of a double Bose-Einstein condensate and, second, the transfer of shallow bound Feshbach molecules to the absolute internal ground state. The production of heteronuclear ground state molecules allows to enter the world of ultracold polar quantum systems.
The capability to reach ultracold atomic temperatures in compact instruments has recently been extended into space. Ultracold temperatures amplify quantum effects, while free-fall allows further cooling and longer interactions time with gravity - the final force without a quantum description. On Earth, these devices have produced macroscopic quantum phenomena such as Bose-Einstein condensation (BECs), superfluidity, and strongly interacting quantum gases. Quantum sensors interfering the superposition of two ultracold atomic isotopes have tested the Universality of Free Fall (UFF), a core tenet of Einstein's classical gravitational theory, at the 10−12 level. In space, cooling the elements needed to explore the rich physics of strong interactions and preparing the multiple species required for quantum tests of the UFF has remained elusive. Here, utilizing upgraded capabilities of the multi-user Cold Atom Lab (CAL) instrument within the International Space Station (ISS), we report the first simultaneous production of a dual species Bose-Einstein condensate in space (formed from 87Rb and 41K), observation of interspecies interactions, as well as the production of 39K ultracold gases. We have further achieved the first space-borne demonstration of simultaneous atom interferometry with two atomic species (87Rb and 41K). These results are an important step towards quantum tests of UFF in space, and will allow scientists to investigate aspects of few-body physics, quantum chemistry, and fundamental physics in novel regimes without the perturbing asymmetry of gravity.