3,799 research outputs found
Periodic shedding of vortex dipoles from a moving penetrable obstacle in a Bose-Einstein condensate
We investigate vortex shedding from a moving penetrable obstacle in a highly
oblate Bose-Einstein condensate. The penetrable obstacle is formed by a
repulsive Gaussian laser beam that has the potential barrier height lower than
the chemical potential of the condensate. The moving obstacle periodically
generates vortex dipoles and the vortex shedding frequency linearly
increases with the obstacle velocity as , where is a
critical velocity. Based on periodic shedding behavior, we demonstrate
deterministic generation of a single vortex dipole by applying a short linear
sweep of a laser beam. This method will allow further controlled vortex
experiments such as dipole-dipole collisions.Comment: 6 pages, 7 figure
Optical pumping effect in absorption imaging of F=1 atomic gases
We report our study of the optical pumping effect in absorption imaging of
Na atoms in the hyperfine spin states. Solving a set of rate
equations for the spin populations in the presence of a probe beam, we obtain
an analytic expression for the optical signal of the absorption imaging.
Furthermore, we verify the result by measuring the absorption spectra of
Na Bose-Einstein condensates prepared in various spin states with
different probe beam pulse durations. The analytic result can be used in the
quantitative analysis of spinor condensate imaging and readily applied to
other alkali atoms with nuclear spin such as Rb.Comment: 6 pages, 4 figure
Collisional Dynamics of Half-Quantum Vortices in a Spinor Bose-Einstein Condensate
We present an experimental study on the interaction and dynamics of
half-quantum vortices (HQVs) in an antiferromagnetic spinor Bose-Einstein
condensate. By exploiting the orbit motion of a vortex dipole in a trapped
condensate, we perform a collision experiment of two HQV pairs, and observe
that the scattering motions of the HQVs is consistent with the short-range
vortex interaction that arises from nonsingular magnetized vortex cores. We
also investigate the relaxation dynamics of turbulent condensates containing
many HQVs, and demonstrate that spin wave excitations are generated by the
collisional motions of the HQVs. The short-range vortex interaction and the
HQV-magnon coupling represent two characteristics of the HQV dynamics in the
spinor superfluid.Comment: 7 pages, 6 figure
Observation of wall-vortex composite defects in a spinor Bose-Einstein condensate
We report the observation of spin domain walls bounded by half-quantum
vortices (HQVs) in a spin-1 Bose-Einstein condensate with antiferromagnetic
interactions. A spinor condensate is initially prepared in the easy-plane polar
phase, and then, suddenly quenched into the easy-axis polar phase. Domain walls
are created via the spontaneous symmetry breaking in the phase
transition and the walls dynamically split into composite defects due to snake
instability. The end points of the defects are identified as HQVs for the polar
order parameter and the mass supercurrent in their proximity is demonstrated
using Bragg scattering. In a strong quench regime, we observe that singly
charged quantum vortices are formed with the relaxation of free wall-vortex
composite defects. Our results demonstrate a nucleation mechanism for composite
defects via phase transition dynamics.Comment: 10 pages, 11 figures, reference update
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