172 research outputs found
Hawking radiation in a two-component Bose-Einstein condensate
We consider a simple realization of an event horizon in the flow of a
one-dimensional two-component Bose-Einstein condensate. Such a condensate has
two types of quasiparticles; In the system we study, one corresponds to density
fluctuations and the other to polarization fluctuations. We treat the case
where a horizon occurs only for one type of quasiparticles (the polarization
ones). We study the one- and two-body signal associated to the analog of
spontaneous Hawking radiation and demonstrate by explicit computation that it
consists only in the emission of polarization waves. We discuss the
experimental consequences of the present results in the domain of atomic
Bose-Einstein condensates and also for the physics of exciton-polaritons in
semiconductor microcavities
Interference effects in the two-dimensional scattering of microcavity polaritons by an obstacle: phase dislocations and resonances
We consider interference effects within the linear description of the
scattering of two-dimensional microcavity polaritons by an obstacle. The
polariton wave may exhibit phase dislocations created by the interference of
the incident and the scattered fields. We describe these structures within the
general framework of singular optics. We also discuss another type of
interference effects appearing due to the formation of (quasi)resonances in the
potential of a repulsive obstacle with sharp boundaries. We discuss the
relevance of our approach for the description of recent experimental results
and propose a criterion for evaluating the importance of nonlinear effects.Comment: 11 pages, 9 figure
Nonlinear waves in coherently coupled Bose-Einstein condensates
We consider a quasi-one-dimensional two-component Bose-Einstein condensate
subject to a coherent coupling between its components, such as realized in
spin-orbit coupled condensates. We study how nonlinearity modifies the dynamics
of the elementary excitations. The spectrum has two branches which are affected
in different ways. The upper branch experiences a modulational instability
which is stabilized by a long wave-short wave resonance with the lower branch.
The lower branch is stable. In the limit of weak nonlinearity and small
dispersion it is described by a Korteweg-de Vries equation or by the Gardner
equation, depending on the value of the parameters of the system
Bogoliubov Theory of acoustic Hawking radiation in Bose-Einstein Condensates
We apply the microscopic Bogoliubov theory of dilute Bose-Einstein
condensates to analyze quantum and thermal fluctuations in a flowing atomic
condensate in the presence of a sonic horizon. For the simplest case of a
step-like horizon, closed-form analytical expressions are found for the
spectral distribution of the analog Hawking radiation and for the density
correlation function. The peculiar long-distance density correlations that
appear as a consequence of the Hawking emission features turns out to be
reinforced by a finite initial temperature of the condensate. The analytical
results are in good quantitative agreement with first principle numerical
calculations.Comment: 11 pages, 7 figure
Polarization hydrodynamics in a one-dimensional polariton condensate
We study the hydrodynamics of a nonresonantly-pumped polariton condensate in
a quasi-one-dimensional quantum wire taking into account the spin degree of
freedom. We clarify the relevance of the Landau criterion for superfluidity in
this dissipative two-component system. Two Cherenkov-like critical velocities
are identified corresponding to the opening of different channels of radiation:
one of (damped) density fluctuations and another of (weakly damped)
polarization fluctuations. We determine the drag force exerted onto an external
obstacle and propose experimentally measurable consequences of the specific
features of the fluctuations of polarization
Wave pattern induced by a localized obstacle in the flow of a one-dimensional polariton condensate
Motivated by recent experiments on generation of wave patterns by a polariton
condensate incident on a localized obstacle, we study the characteristics of
such flows under the condition that irreversible processes play a crucial role
in the system. The dynamics of a non-resonantly pumped polariton condensate in
a quasi-one-dimensional quantum wire is modeled by a Gross-Pitaevskii equation
with additional phenomenological terms accounting for the dissipation and
pumping processes. The response of the condensate flow to an external potential
describing a localized obstacle is considered in the weak-perturbation limit
and also in the nonlinear regime. The transition from a viscous drag to a
regime of wave resistance is identified and studied in detail
Dipole Oscillations of a Bose-Einstein Condensate in Presence of Defects and Disorder
We consider dipole oscillations of a trapped dilute Bose-Einstein condensate
in the presence of a scattering potential consisting either in a localized
defect or in an extended disordered potential. In both cases the breaking of
superfluidity and the damping of the oscillations are shown to be related to
the appearance of a nonlinear dissipative flow. At supersonic velocities the
flow becomes asymptotically dissipationless.Comment: 4 pages, 4 figure
Bose beams: coherent propagation through a guide
We compute the stationary profiles of a coherent beam of Bose condensed atoms
propagating through a guide. Special emphasis is put on the effect of an
obstacle present on the trajectory of the beam. The obstacle considered (such
as a bend in the guide, or a laser field perpendicular to the beam) results in
a repulsive or an attractive potential acting on the condensate. Different
behaviors are observed when varying the beam velocity (with respect to the
speed of sound), the size of the obstacle (relative to the healing length) and
the intensity and sign of the potential. The existence of bound states of the
condensate is also considered.Comment: 32 pages, 13 figures final version, typos corrected and better
discussion of the boundary condition
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