Theory of the Ramsey spectroscopy and anomalous segregation in ultra-cold rubidium

Abstract

The recent anomalous segregation experiment of Lewandowski et al. (PRL, 88, 070403, 2002) shows dramatic, rapid internal state segregation for two hyperfine levels of rubidium. We simulate an effective one dimensional model of the system for experimental parameters and find reasonable agreement with the data. The Ramsey frequency is found to be insensitive to the decoherence of the superposition, and is only equivalent to the interaction energy shift for a pure superposition. A Quantum Boltzmann equation describing collisions is derived using Quantum Kinetic Theory, taking into account the different scattering lengths of the internal states. As spin-wave experiments are likely to be attempted at lower temperatures we examine the effect of degeneracy on decoherence by considering the recent experiment of Lewandowski et al. where degeneracy is around 10%. We also find that the segregation effect is only possible when transport terms are included in the equations of motion, and that the interactions only directly alter the momentum distributions of the states. The segregation or spin wave effect is thus entirely due to coherent atomic motion as foreseen in the experimental report

26 pages, 4 figures, to be published in J. Phys. B

References in corpus (7)

• Observation of anomalous spin-state segregation in a trapped ultra-cold vapor
• Spatial resolution of spin waves in an ultra-cold gas
• Signatures of resonance superfluidity in a quantum Fermi gas
• Internal state conversion in ultracold gases
• Internal waves and synchronized precession in a cold vapor
• Longitudinal spin waves in a dilute Bose gas
• Theory of the cold collision frequency shift in 1S--2S spectroscopy of Bose-Einstein-condensed and non-condensed hydrogen

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• Demagnetization dynamics of non-interacting trapped fermions
• Spin Diffusion in Trapped Gases: Anisotropy in Dipole and Quadrupole Modes
• Anisotropic Spin Diffusion in Trapped Boltzmann Gases
• Effect of trap symmetry and atom-atom interactions on a trapped atom interferometer with internal state labelling