169 research outputs found

    Comment on the paper: Quantum backaction of optical observations on Bose-Einstein condensates by U. Leonhardt, T. Kiss, and P. Piwnicki, Eur. Phys. J. D7, 413 (1999)

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    A recent paper, Quantum backaction of optical observations on Bose-Einstein condensates by U. Leonhardt, T. Kiss, and P. Piwnicki, Eur. Phys. J. D7, 413 (1999), emphasized that the limit of dispersive imaging of Bose-Einstein condensates with off-resonant light is not residual absorption, but a different form of quantum backaction of the probe light. This note points out that these conclusions are incorrect, and that Rayleigh scattering is the dominant quantum backaction of dispersive imaging.Comment: 1 page (Comment on paper

    A Distributed GUI-based Computer Control System for Atomic Physics Experiments

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    Atomic physics experiments often require a complex sequence of precisely timed computer controlled events. A distributed GUI-based control system designed with such experiments in mind, The Cicero Word Generator, is described. The system makes use of a client-server separation between a user interface for sequence design and a set of output hardware servers. Output hardware servers are designed to use standard National Instruments output cards, but the client-server nature allows this to be extended to other output hardware. Output sequences running on multiple servers and output cards can be synchronized using a shared clock. By using an FPGA-generated variable frequency clock, redundant buffers can be dramatically shortened, and a time resolution of 100ns achieved over effectively arbitrary sequence lengths

    A simple model for interactions and corrections to the Gross-Pitaevskii Equation

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    One of the assumptions leading to the Gross-Pitaevskii Equation (GPE) is that the interaction between atom pairs can be written effectively as a \delta -function so that the interaction range of the particles is assumed to vanish. A simple model that takes into account the extension of the inter-particle potential is introduced. The correction to the GPE predictions for the energy of a condensate confined by a harmonic trap in the Thomas-Fermi (TF) regime is estimated. Although it is found to be small, we believe that in some situations it can be measured using its dependance on the frequency of the confining trap. Due to the simplicity of the model, it may have a wide range of applications.Comment: 22 pages, 2 figure

    Collective enhancement and suppression in Bose-Einstein condensates

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    The coherent and collective nature of Bose-Einstein condensate can enhance or suppress physical processes. Bosonic stimulation enhances scattering in already occupied states which leads to atom amplification, and the suppression of dissipation leads to superfluidity. In this paper, we review several experiments where suppression and enhancement have been observed and discuss the common roots of and differences between these phenomena.Comment: ICAP proceedings; 12 figure

    Experiments with Ultracold Quantum-degenerate Fermionic Lithium Atoms

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    Experimental methods of laser and evaporative cooling, used in the production of atomic Bose-Einstein condensates have recently been extended to realize quantum degeneracy in trapped Fermi gases. Fermi gases are a new rich system to explore the implications of Pauli exclusion on scattering properties of the system, and ultimately fermionic superfluidity. We have produced a new macroscopic quantum system, in which a degenerate Li-6 Fermi gas coexists with a large and stable Na-23 BEC. This was accomplished using inter-species sympathetic cooling of fermionic 6Li in a thermal bath of bosonic Na-23. We have achieved high numbers of both fermions (less than 10(exp 5) and bosons (less than 10(exp 6), and Li-6 quantum degeneracy corresponding to one half of the Fermi temperature. This is the first time that a Fermi sea was produced with a condensate as a "refrigerator"

    Correlations and Pair Formation in a Repulsively Interacting Fermi Gas

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    A degenerate Fermi gas is rapidly quenched into the regime of strong effective repulsion near a Feshbach resonance. The spin fluctuations are monitored using speckle imaging and, contrary to several theoretical predictions, the samples remain in the paramagnetic phase for arbitrarily large scattering length. Over a wide range of interaction strengths a rapid decay into bound pairs is observed over times on the order of 10\hbar/E_F, preventing the study of equilibrium phases of strongly repulsive fermions. Our work suggests that a Fermi gas with strong short-range repulsive interactions does not undergo a ferromagnetic phase transition
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