2009/12/17 by R. Sarjonen, Sarjonen, R., M. Saarela +3
Physics and Astronomy · #Cold Atom Physics and Bose-Einstein Condensates #FOS: Physical sciences #Optical properties and cooling technologies in crystalline materials #Quantum Gases (cond-mat.quant-gas) #Quantum, superfluid, helium dynamics #cond-mat.quant-gas
paper · pdf · doi:10.48550/arxiv.0912.3336
5 pages containing 5 figures
arxiv created 2009/12/17 · openalex publication_date 2009/12/17 · arxiv updated 2010/01/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We present a theoretical analysis of excitation modes in Bose-Einstein condensates in ultracold alkali-metal gases for large scattering lengths and momenta where corrections to the mean field approximation become important. We assume that the effective interaction in the metastable, single channel, gaseous phase has a well defined Fourier transform that scales with the scattering length. Based on this we show that for increasing scattering lengths or equivalently increasing densities the system becomes less correlated and that at large values of the scattering length Bragg scattering measures directly the Fourier transform of the effective two-body potential. We construct model potentials which fit the recently measured line shifts in 85Rb by Papp et al. (Phys. Rev. Lett. \bf 101, 135301 (2008)), and show that they fix the low momentum expansion of the effective range function. We find excellent agreement with the experimental data when the effective range is ≪ 1 and the coefficient of the k4-term is -7.5 ± 0.5 in scattering length units. The resolution in Bragg scattering experiments so far does not reveal details of the frequency dependence in the dynamic structure function S(k,ω) and we show that the Feynman spectrum determines the measured line shifts. We propose the possibility of a transition to a novel density wave state.