1,268 research outputs found
Coherent Collisions between Bose-Einstein Condensates
We study the non-degenerate parametric amplifier for matter waves,
implemented by colliding two Bose-Einstein condensates. The coherence of the
amplified waves is shown by observing high contrast interference with a
reference wave and by reversing the amplification process. Since our
experiments also place limits on all known sources of decoherence, we infer
that relative number squeezing is most likely present between the amplified
modes. Finally, we suggest that reversal of the amplification process may be
used to detect relative number squeezing without requiring single-particle
detection.Comment: 4.2 pages, 4 figures, please take postscript version for best quality
of picture
Effective one-component description of two-component Bose-Einstein condensate dynamics
We investigate dynamics in two-component Bose-Einstein condensates in the
context of coupled Gross-Pitaevskii equations and derive results for the
evolution of the total density fluctuations. Using these results, we show how,
in many cases of interest, the dynamics can be accurately described with an
effective one-component Gross-Pitaevskii equation for one of the components,
with the trap and interaction coefficients determined by the relative
differences in the scattering lengths. We discuss the model in various regimes,
where it predicts breathing excitations, and the formation of vector solitons.
An effective nonlinear evolution is predicted for some cases of current
experimental interest. We then apply the model to construct quasi-stationary
states of two-component condensates.Comment: 8 pages, 4 figure
Enhanced heat flow in the hydrodynamic-collisionless regime
We study the heat conduction of a cold, thermal cloud in a highly asymmetric
trap. The cloud is axially hydrodynamic, but due to the asymmetric trap
radially collisionless. By locally heating the cloud we excite a thermal dipole
mode and measure its oscillation frequency and damping rate. We find an
unexpectedly large heat conduction compared to the homogeneous case. The
enhanced heat conduction in this regime is partially caused by atoms with a
high angular momentum spiraling in trajectories around the core of the cloud.
Since atoms in these trajectories are almost collisionless they strongly
contribute to the heat transfer. We observe a second, oscillating hydrodynamic
mode, which we identify as a standing wave sound mode.Comment: Sumitted to Phys. Rev. Letters, 4 pages, 4 figure
Reaching the hydrodynamic regime in a Bose-Einstein condensate by suppression of avalanche
We report the realization of a Bose-Einstein condensate (BEC) in the
hydrodynamic regime. The hydrodynamic regime is reached by evaporative cooling
at a relative low density suppressing the effect of avalanches. With the
suppression of avalanches a BEC containing 120.10^6 atoms is produced. The
collisional opacity can be tuned from the collisionless regime to a collisional
opacity of more than 3 by compressing the trap after condensation. In the
collisional opaque regime a significant heating of the cloud at time scales
shorter than half of the radial trap period is measured. This is direct proof
that the BEC is hydrodynamic.Comment: Article submitted for Phys. Rev. Letters, 6 figure
Large atom number Bose-Einstein condensate of sodium
We describe the setup to create a large Bose-Einstein condensate containing
more than 120x10^6 atoms. In the experiment a thermal beam is slowed by a
Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical
dark-spot MOT in our experiments contains 2.0x10^10 atoms with a temperature of
320 microK and a density of about 1.0x10^11 atoms/cm^3. The sample is spin
polarized in a high magnetic field, before the atoms are loaded in the magnetic
trap. Spin polarizing in a high magnetic field results in an increase in the
transfer efficiency by a factor of 2 compared to experiments without spin
polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s by
evaporative cooling. To suppress the 3-body losses at the end of the
evaporation the magnetic trap is decompressed in the axial direction.Comment: 11 pages, 12 figures, submitted to Review Of Scientific Instrument
Training deep neural density estimators to identify mechanistic models of neural dynamics
Mechanistic modeling in neuroscience aims to explain observed phenomena in terms of underlying causes. However, determining which model parameters agree with complex and stochastic neural data presents a significant challenge. We address this challenge with a machine learning tool which uses deep neural density estimators-- trained using model simulations-- to carry out Bayesian inference and retrieve the full space of parameters compatible with raw data or selected data features. Our method is scalable in parameters and data features, and can rapidly analyze new data after initial training. We demonstrate the power and flexibility of our approach on receptive fields, ion channels, and Hodgkin-Huxley models. We also characterize the space of circuit configurations giving rise to rhythmic activity in the crustacean stomatogastric ganglion, and use these results to derive hypotheses for underlying compensation mechanisms. Our approach will help close the gap between data-driven and theory-driven models of neural dynamics
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