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arXiv:1003.5734 · Physical Review A

Roughness with a finite correlation length in a microtrap

Muzhi Wu, Xiaoji Zhou, W. M. Liu, Xuzong Chen

Published Mar 29, 2010• 1 citation
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Abstract

We analyze the effects of roughness in the magnitude of the magnetic field produced by a current carrying microwire, which is caused by the geometric fluctuation of the edge of the wire. The relation between the fluctuation of the trapping potential and the height the atom trap lies above the wire is very well consistent with the experimental data when the colored noise with a finite correlation length is considered. On this basis, we generate the random potential and get the density distribution of the Bose-Einstein condensate (BEC) atoms by solving the Gross-Pitaevskii equation, which coincides well with the experimental image, especially in the number of fragmentations. The results help us further understand the nature of the fluctuation and predict its possible application in the precise measurement.

DOI
10.1103/physreva.81.033625

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We analyze the effects of roughness in the magnitude of the magnetic field produced by a current carrying microwire, which is caused by the geometric fluctuation of the edge of the wire. The relation between the fluctuation of the trapping potential and the height the atom trap lies above the wire is very well consistent with the experimental data when the colored noise with a finite correlation length is considered. On this basis, we generate the random potential and get the density distribution of the Bose-Einstein condensate (BEC) atoms by solving the Gross-Pitaevskii equation, which coincides well with the experimental image, especially in the number of fragmentations. The results help us further understand the nature of the fluctuation and predict its possible application in the precise measurement.
We analyze the effects of a random magnetic potential in a microfabricated waveguide for ultracold atoms. We find that the shape and position fluctuations of a current carrying wire induce a strong Gaussian correlated random potential with a length scale set by the atom-wire separation. The theory is used to explain quantitatively the observed fragmentation of the Bose-Einstein condensates in atomic waveguides. Furthermore, we show that nonlinear dynamics can be used to provide important insights into the nature of the strongly fragmented condensates. We argue that a quantum phase transition from the superfluid to the insulating Bose glass phase may be reached and detected under the realistic experimental conditions.
We systematically investigate the properties of the quenched disorder potential in an atomic waveguide, and study its effects to the dynamics of condensate in the strong disorder region. We show that even very small wire shape fluctuations can cause strong disorder potential along the wire direction, leading to the fragmentation phenomena as the condensate is close to the wire surface. The generic disorder potential is Gaussian correlated random potential with vanishing correlations in both short and long wavelength limits and with a strong correlation weight at a finite length scale, set by the atom-wire distance. When the condensate is fragmentized, we investigate the coherent and incoherent dynamics of the condensate, and demonstrate that it can undergo a crossover from a coherent condensate to an insulating Bose-glass phase in strong disorder (or low density) regime. Our numerical results obtained within the meanfield approximation are semi-quantitatively consistent with the experimental results.
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Atom chips use current flowing in lithographically patterned wires to produce microscopic magnetic traps for atoms. The density distribution of a trapped cold atom cloud reveals disorder in the trapping potential, which results from meandering current flow in the wire. Roughness in the edges of the wire is usually the main cause of this behaviour. Here, we point out that the edges of microfabricated wires normally exhibit self-affine roughness. We investigate the consequences of this for disorder in atom traps. In particular, we consider how closely the trap can approach the wire when there is a maximum allowable strength of the disorder. We comment on the role of roughness in future atom--surface interaction experiments.
Atom chips use current flowing in lithographically patterned wires to produce microscopic magnetic traps for atoms. The density distribution of a trapped cold atom cloud reveals disorder in the trapping potential, which results from meandering current flow in the wire. Roughness in the edges of the wire is usually the main cause of this behaviour. Here, we point out that the edges of microfabricated wires normally exhibit self-affine roughness. We investigate the consequences of this for disorder in atom traps. In particular, we consider how closely the trap can approach the wire when there is a maximum allowable strength of the disorder. We comment on the role of roughness in future atom–surface interaction experiments.