2,699 research outputs found
Band Gap Closing in a Synthetic Hall Tube of Neutral Fermions
We report the experimental realization of a synthetic three-leg Hall tube
with ultracold fermionic atoms in a one-dimensional optical lattice. The legs
of the synthetic tube are composed of three hyperfine spin states of the atoms,
and the cyclic inter-leg links are generated by two-photon Raman transitions
between the spin states, resulting in a uniform gauge flux penetrating
each side plaquette of the tube. Using quench dynamics, we investigate the band
structure of the Hall tube system for a commensurate flux .
Momentum-resolved analysis of the quench dynamics reveals that a critical point
of band gap closing as one of the inter-leg coupling strengths is varied, which
is consistent with a topological phase transition predicted for the Hall tube
system.Comment: 8 pages, 8 figure
Metastable hard-axis polar state of a spinor Bose-Einstein condensate under a magnetic field gradient
We investigate the stability of a hard-axis polar state in a spin-1
antiferromagnetic Bose-Einstein condensate under a magnetic field gradient,
where the easy-plane spin anisotropy is controlled by a negative quadratic
Zeeman energy . In a uniform magnetic field, the axial polar state is
dynamically unstable and relaxes into the planar polar ground state. However,
under a field gradient , the excited spin state becomes metastable down to
a certain threshold and as decreases below , its intrinsic
dynamical instability is rapidly recalled. The incipient spin excitations in
the relaxation dynamics appear with stripe structures, indicating the
rotational symmetry breaking by the field gradient. We measure the dependences
of on and the sample size, and we find that is highly
sensitive to the field gradient in the vicinity of , exhibiting power-law
behavior of with . Our results
demonstrate the significance of the field gradient effect in the quantum
critical dynamics of spinor condensates.Comment: 8 pages, 7 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
Creating walk-through images from a video sequence of a dynamic scene
A comprehensive scheme for creating walk-through images from a video sequence by generalizing the idea of tour into the picture (TIP) was discussed. The proposed scheme was designed to incorporate a new modeling scheme on a vanishing circle identified in the video and an automatic background detection from the video. This scheme let users experience the feel of navigating into a video sequence with their own interpretation and imagination about a given scene. The proposed scheme covers several types of video films of dynamic scenes such as sports coverage, cartoon animation and movie films in which object continuously change shapes and locations
Double resonance of Raman transitions in a degenerate Fermi gas
We measure momentum-resolved Raman spectra of a spin-polarized degenerate
Fermi gas of Yb atoms for a wide range of magnetic fields, where the
atoms are irradiated by a pair of counterpropagating Raman laser beams as in
the conventional spin-orbit coupling scheme. Double resonance of first- and
second-order Raman transitions occurs at a certain magnetic field and the
spectrum exhibits a doublet splitting for high laser intensities. The measured
spectral splitting is quantitatively accounted for by the Autler-Townes effect.
We show that our measurement results are consistent with the spinful band
structure of a Fermi gas in the spatially oscillating effective magnetic field
generated by the Raman laser fields.Comment: 7 pages, 6 figure
Observation of a Geometric Hall Effect in a Spinor Bose-Einstein Condensate with a Skyrmion Spin Texture
For a spin-carrying particle moving in a spatially varying magnetic field,
effective electromagnetic forces can arise due to the geometric phase
associated with adiabatic spin rotation of the particle. We report the
observation of a geometric Hall effect in a spinor Bose-Einstein condensate
with a skyrmion spin texture. Under translational oscillations of the spin
texture, the condensate resonantly develops a circular motion in a harmonic
trap, demonstrating the existence of an effective Lorentz force. When the
condensate circulates, quantized vortices are nucleated in the boundary region
of the condensate and the vortex number increases over 100 without significant
heating. We attribute the vortex nucleation to the shearing effect of the
effective Lorentz force from the inhomogeneous effective magnetic field.Comment: 9 pages, 11 figure
Creutz ladder in a resonantly shaken 1D optical lattice
We report the experimental realization of a Creutz ladder for ultracold fermionic atoms in a resonantly driven 1D optical lattice. The two-leg ladder consists of the two lowest orbital states of the optical lattice and the cross inter-leg links are generated via two-photon resonant coupling between the orbitals by periodic lattice shaking. The characteristic pseudo-spin winding structure in the energy bands of the ladder system is demonstrated using momentum-resolved Ramsey-type interferometric measurements. We discuss a two-tone driving method to extend the inter-leg link control and propose a topological charge pumping scheme for the Creutz ladder system. ©2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaf
- …