We describe the setup to create a large Bose-Einstein condensate containing more than 120·10 6 atoms. In the experiment a thermal beam is slowed by a Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical dark-spot MOT in our experiments contains 2.0·10 10 atoms with a temperature of 320 µK and a density of about 1.0·10 11 atoms/cm 3 . The sample is spin polarized in a high magnetic field, before the atoms are loaded in the magnetic trap. Spin polarizing in a high magnetic field results in an increase in the transfer efficiency by a factor of 2 compared to experiments without spin polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s by evaporative cooling. To suppress the 3-body losses at the end of the evaporation the magnetic trap is decompressed in the axial direction.

An approximated form of the Dyson-Schwinger equation for the gluon propagator in quarkless QCD is subjected to nonlinear functional and numerical analysis. It is found that solutions exist, and that these have a double pole at the origin of the square of the propagator momentum, together with an accumulation of soft branch points. This analytic structure is strongly suggestive of confinement by infrared slavery.

We report on the experimental investigation of the response of a three-dimensional Bose-Einstein condensate (BEC) in the presence of a one-dimensional (1D) optical lattice. By means of Bragg spectroscopy we probe the band structure of the excitation spectrum in the presence of the periodic potential. We selectively induce elementary excitations of the BEC choosing the transferred momentum and we observe different resonances in the energy transfer, corresponding to the transitions to different bands. The frequency, the width and the strength of these resonances are investigated as a function of the amplitude of the 1D optical lattice.PACS numbers: 67.85. Hj, 67.85.De The knowledge of the linear response of a complex system gives crucial information about its many-body behavior. For example, the superfluid properties of a three-dimensional (3D) Bose-Einstein condensate (BEC) are related to the linear part of the phononic dispersion relation at low momenta [1]. The presence of optical lattices enriches the excitation spectrum of a BEC in a remarkable way. For deep three-dimensional lattices, the gas enters the strongly correlated Mott insulator phase and the spectrum exhibits a gap at low energies [2]. The response of a BEC in the superfluid phase is also drastically modified by the presence of a one-dimensional (1D) optical lattice [3,4,5,6,7]. Indeed, as in any periodic system, energy gaps open in the spectrum at the multiples of the lattice momentum and it is possible to excite several states corresponding to different energy bands at a given value of the momentum transfer [8,9]. In addition, the linear dispersion relation of the superfluid, and thus its sound velocity, is changed. In the mean-field regime of interactions these peculiar features of the excitations of a superfluid BEC in the presence of an optical lattice are captured by the Bogoliubov theory [1].Bragg spectroscopy represents an excellent experimental tool to investigate the linear response of gaseous BECs [10]. It has allowed to measure the dispersion relation of interacting BECs in the mean-field regime [11,12,13] In this work we use Bragg spectroscopy to probe the excitation spectrum of a 3D BEC loaded in a 1D optical lattice. Previous experimental studies have so far investigated the excitations of superfluid BECs within the lowest energy band of a 3D optical lattice by means of lattice modulation [19] and Bragg spectroscopy [18,20]. This paper presents a detailed experimental study of the different bands in the excitation spectrum of an interacting 3D BEC in the presence of a 1D optical lattice. We measure the resonance frequencies, the strengths and the widths of the transitions to different bands of the 1D optical lattice. The measurements are quantitatively compared with Bogoliubov mean-field calculations for our experimental system [7]. We produce a 3D cigar-shaped BEC of N≃ 3 × 10 5 87 Rb atoms in a Ioffe-Pritchard magnetic trap whose

We use a two-color lattice to break the homogeneous site occupation of an atomic Mott insulator of bosonic 87Rb. We detect the disruption of the ordered Mott domains via noise correlation analysis of the atomic density distribution after time of flight. The appearance of additional correlation peaks evidences the redistribution of the atoms into a strongly inhomogeneous insulating state, in quantitative agreement with the predictions.

We report the realization of a Bose-Einstein condensate (BEC) in the hydrodynamic regime. The hydrodynamic regime is reached by evaporative cooling at a relative low density suppressing the effect of avalanches. With the suppression of avalanches a BEC containing 120·10 6 atoms is produced. The collisional opacity can be tuned from the collisionless regime to a collisional opacity of more than 3 by compressing the trap after condensation. In the collisional opaque regime a significant heating of the cloud at time scales shorter than half of the radial trap period is measured. This is direct proof that the BEC is hydrodynamic.PACS numbers: 03.75. Kk,32.80.Pj The behavior of excitations in a BEC with energies larger than the mean field energy is determined by the mean free path of the atoms. Usually the mean free path of the atoms is larger than the size of the sample (the collisionless regime). It would be of great interest to realize a BEC in the hydrodynamic regime, where the mean free path of the atom is less than the size of the condensate. In this situation the properties of the BEC are strongly influenced by the inter-atomic collisions. A hydrodynamic BEC would give the opportunity to investigate interesting properties of the condensate, for example, thermal excitations, heat conduction, shape oscillations, when there is only locally thermal equilibrium.The transition from the collisionless to the hydrodynamic regime above the BEC transition temperature has been studied theoretically [1] and experimentally [2]. For the situation below the BEC transition temperature theoretical discussions are given in Refs. [3,4,5,6]. In this Letter we will discuss the experimental realization of a BEC in the hydrodynamic regime and study the excitations generated by three-body decay.The most obvious way of reaching the hydrodynamic regime is creating a large and dense BEC. However, like shown in Ref. [7] the atom losses will increase strongly due to avalanches at such high densities, that are normally necessary for entering the hydrodynamic regime. This will severely limit the lifetime of the condensate in the hydrodynamic regime, as well as the collisional opacity. Therefore, Schuster et al. [7] concluded that the collisionally opaque regime can hardly be reached in alkali BEC experiments. In the case of metastable helium BEC experiments to reach the hydrodynamic regime has so far been unsuccessful [8,9]. A second way of realizing a hydrodynamic BEC is increasing the cross section for the elastic collisions by means of a Feshbach resonance. The increase in the cross section results in a large loss rate [10], which makes it an unsuitable approach for achieving a hydrodynamic BEC. Notable exceptions are the BEC's of molecules consisting of fermions tuned close to the unitarity limit [11].In this Letter we will show that it is possible to enter the hydrodynamic regime by following the first approach with a strong reduction of the effects of the problems mentioned above. This is done by evaporative cooling a cloud of atoms...