Bragg spectroscopy of 1D and 3D Bose Einstein condensates in optical lattices

This work is focused on the Bragg spectroscopy [1] of a Bose Einstein condensate loaded in optical lattices: we investigate an elongated 3D condensate and a set of 1D uncoupled tubes, in the presence of an optical lattice in the same longitudinal direction. The Bragg spectroscopy allows exploring the linear response of the system to external excitations, which gives important information about its properties: we induce a large energy and momentum transfer, and we measure single-particle excitation spectrum and dynamical structure factor [2]. The resonance frequency and the transition strength in the presence of the longitudinal optical lattice are well described by a mean-field theory both in 1D and in 3D case [3]; while the resonance width is connected to the coherence properties of the system. To highlight the important role of correlation in the 1D case [4] we also investigated the 3D-1D crossover by varying the optical confinement of each 1D tube, without superimposing a longitudinal lattice. -- References: [1] J. Stenger et al., Physical Review Letters 82, 4569 (1999). [2] F. Zambelli et al., Physical Review A 61, 063608 (2000). [3] C. Menotti et al., Physical Review A 67, 053609 (2003). [4] B. Laburthe Tolra et al., Physical Review Letters 92, 190401 (2004).