We present highly efficient emission of twin-atom beams into a single transversal mode of a waveguide potential. The source is a one-dimensional degenerate Bose gas in the first radially excited state. We directly measure a suppression of fluctuations in the atom number difference between the beams to 0.37(3) with respect to the classical expectation, equivalent to 0.11(2) after correcting for detection noise. Our results underline the high potential of ultracold atomic gases as sources for quantum matter wave optics and will enable the implementation of schemes previously unattainable with massive particlesComment: 7 pages (including supplementary material), 5 figure

We investigate theoretically the evolution of the two-point density correlation function of a low-dimensional ultracold Bose gas after release from a tight transverse confinement. In the course of expansion thermal and quantum fluctuations present in the trapped systems transform into density fluctuations. For the case of free ballistic expansion relevant to current experiments, we present simple analytical relations between the spectrum of "density ripples" and the correlation functions of the original confined systems. We analyze several physical regimes, including weakly and strongly interacting one-dimensional ͑1D͒ Bose gases and twodimensional ͑2D͒ Bose gases below the Berezinskii-Kosterlitz-Thouless ͑BKT͒ transition. For weakly interacting 1D Bose gases, we obtain an explicit analytical expression for the spectrum of density ripples which can be used for thermometry. For 2D Bose gases below the BKT transition, we show that for sufficiently long expansion times the spectrum of the density ripples has a self-similar shape controlled only by the exponent of the first-order correlation function. This exponent can be extracted by analyzing the evolution of the spectrum of density ripples as a function of the expansion time.

We measure the two-point density correlation function of freely expanding quasicondensates in the weakly interacting quasi-one-dimensional (1D) regime. While initially suppressed in the trap, density fluctuations emerge gradually during expansion as a result of initial phase fluctuations present in the trapped quasicondensate. Asymptotically, they are governed by the thermal coherence length of the system. Our measurements take place in an intermediate regime where density correlations are related to near-field diffraction effects and anomalous correlations play an important role. Comparison with a recent theoretical approach described by Imambekov et al. yields good agreement with our experimental results and shows that density correlations can be used for thermometry of quasicondensates.

We realize a one-dimensional Josephson junction using quantum degenerate Bose gases in a tunable double well potential on an atom chip. Matter wave interferometry gives direct access to the relative phase field, which reflects the interplay of thermally driven fluctuations and phase locking due to tunneling. The thermal equilibrium state is characterized by probing the full statistical distribution function of the two-point phase correlation. Comparison to a stochastic model allows to measure the coupling strength and temperature and hence a full characterization of the system.Josephson dynamics between weakly coupled macroscopic wave functions have been observed in superconductors [1,2], superfluid Helium [3,4], and recently using Bose-Einstein condensates in double well potentials [5][6][7]. The bosonic Josephson junction (BJJ) is especially interesting, as particle interactions lead to additional dynamical modes such as quantum self trapping or π phase modes [5,8] and finite temperature leads to enhanced fluctuations of the observables [9]. In contrast to other implementations, the BJJ enables complete experimental control over all relevant system parameters such as the coupling strength or relative population together with direct access to the conjugate observables number and phase. Theoretical work has mostly employed a twomode approach to describe the finite temperature equilibrium system and dynamical properties [8,10].One-dimensional (1D) Josephson junctions show a significantly enriched physical behavior, as the two involved wave functions can not be described by single quantum modes any more. The non-interacting 1D junction represents an implementation of the Sine-Gordon Hamiltonian which occurs in widespread areas of physics [11,12]. In the 1D bosonic junction interactions and finite temperature are expected to cause dynamical instabilities of the classical Josephson modes [13]. Whether quasi-static phenomena such as quantum self-trapping persist in 1D is issue of ongoing discussion [14].In this work we realize and fully characterize a onedimensional bosonic Josephson junction using quantum degenerate Bose gases in a tunable double well potential. The finite temperature equilibrium state is marked by the competing effects of thermally driven phase fluctuations and phase locking due to tunnel coupling. Fluctuations of the relative population are < 1 % and can be neglected [9]. We probe the coherence properties of the coupled system by performing matter wave interferometry. Comparing the statistical distribution function of twopoint phase correlations to a stochastic model [10,15], we measure the coupling energy or the temperature of [16,17]. We characterize two-point phase correlations of the system by measuring the statistical properties of the difference of relative phases ∆ϕ(z) = ϕ(z) − ϕ(z ).the system.The experiments are performed in a horizontally orientated double well potential, generated on an atom chip using radio-frequency (RF) induced adiabatic states [18,19]. Different double well paramet...