13 research outputs found
Control of an atom laser using feedback
A generalised method of using feedback to control Bose-Einstein condensates
is introduced. The condensates are modelled by the Gross-Pitaevskii equation,
so only semiclassical fluctations can be suppressed, and back-action from the
measurement is ignored. We show that for any available control, a feedback
scheme can be found to reduce the energy while the appropriate moment is still
dynamic. We demonstrate these schemes by considering a condensate trapped in a
harmonic potential that can be modulated in strength and position. The
formalism of our feedback scheme also allows the inclusion of certain types of
non-linear controls. If the non-linear interaction between the atoms can be
controlled via a Feshbach resonance, we show that the feedback process can
operate with a much higher efficiency.Comment: 6 pages, 7 figure
Density correlations and dynamical Casimir emission of Bogoliubov phonons in modulated atomic Bose-Einstein condensates
We present a theory of the density correlations that appear in an atomic
Bose-Einstein condensate as a consequence of the dynamical Casimir emission of
pairs of Bogoliubov phonons when the atom-atom scattering length is modulated
in time. Different regimes as a function of the temporal shape of the
modulation are identified and a simple physical picture of the phenomenon is
discussed. Analytical expressions for the density correlation function are
provided for the most significant limiting cases. This theory is able to
explain some unexpected features recently observed in numerical calculations of
Hawking radiation from analog black holes
Nonlinear delocalization on disordered Stark ladder
05.45.-a Nonlinear dynamics and chaos, 63.50.-x Vibrational states in disordered systems, 03.75.Kk Dynamic properties of condensates; collective and hydrodynamic excitations, superfluid flow,