43 research outputs found
Localization of a Bose-Fermi mixture in a bichromatic optical lattice
We study the localization of a cigar-shaped super-fluid Bose-Fermi mixture in
a quasi-periodic bichromatic optical lattice (OL) for inter-species attraction
and intra-species repulsion. The mixture is described by the Gross-Pitaevskii
equation for the bosons, coupled to a hydrodynamic mean-field equation for
fermions at unitarity. We confirm the existence of the symbiotic localized
states in the Bose-Fermi mixture and Anderson localization of the Bose
component in the interacting Bose-Fermi mixture on a bichromatic OL. The phase
diagram in boson and fermion numbers showing the regions of the symbiotic and
Anderson localization of the Bose component is presented. Finally, the
stability of symbiotic and Anderson localized states is established under small
perturbations
Symmetry breaking in a localized interacting binary BEC in a bi-chromatic optical lattice
By direct numerical simulation of the time-dependent Gross-Pitaevskii
equation using the split-step Fourier spectral method we study different
aspects of the localization of a cigar-shaped interacting binary
(two-component) Bose-Einstein condensate (BEC) in a one-dimensional
bi-chromatic quasi-periodic optical-lattice potential, as used in a recent
experiment on the localization of a BEC [Roati et al., Nature 453, 895 (2008)].
We consider two types of localized states: (i) when both localized components
have a maximum of density at the origin x=0, and (ii) when the first component
has a maximum of density and the second a minimum of density at x=0. In the
non-interacting case the density profiles are symmetric around x=0. We
numerically study the breakdown of this symmetry due to inter-species and
intra-species interaction acting on the two components. Where possible, we have
compared the numerical results with a time-dependent variational analysis. We
also demonstrate the stability of the localized symmetry-broken BEC states
under small perturbation.Comment: 9 page
Localization of a spin-orbit coupled Bose-Einstein condensate in a bichromatic optical lattice
We study the localization of a noninteracting and weakly interacting
Bose-Einstein condensate with spin-orbit coupling loaded in a quasiperiodic
bichromatic optical lattice potential using the numerical solution and
variational approximation of a binary mean-field Gross-Pitaevskii equation with
two pseudo-spin components. We confirm the existence of the stationary
localized states in the presence of the spin-orbit and Rabi couplings for an
equal distribution of atoms in the two components. We find that the interaction
between the spin-orbit and Rabi couplings favors the localization or
delocalization of the BEC depending on the the phase difference between the
components. We also studied the oscillation dynamics of the localized states
for an initial population imbalance between the two components
Localization of collisionally inhomogeneous condensates in a bichromatic optical lattice
By direct numerical simulation and variational solution of the
Gross-Pitaevskii equation, we studied the stationary and dynamic
characteristics of a cigar-shaped, localized, collisionally inhomogeneous
Bose-Einstein condensate trapped in a one-dimensional bichromatic
quasi-periodic optical-lattice potential, as used in a recent experiment on the
localization of a Bose-Einstein condensate
[Roati et al., Nature (London) {\bf 453}, 895 (2008)]. The effective
potential characterizing the spatially modulated nonlinearity is obtained. It
is found that the collisional inhomogeneity has influence not only on the
central region but also on the tail of the Bose-Einstein condensate. The
influence depends on the sign and value of the spatially modulated nonlinearity
coefficient. We also demonstrate the stability of the stationary localized
stat$ performing a standard linear stability analysis. Where possible, the
numerical results are shown to be in good agreement with the variational
results
Matter-wave localization in a weakly perturbed optical lattice
By numerical solution and variational approximation of the Gross-Pitaevskii
equation, we studied the localization of a noninteracting and
weakly-interacting Bose-Einstein condensate in a weakly perturbed optical
lattice in one and three dimensions. The perturbation achieved through a weak
delocalizing expulsive or a linear potential as well as a weak localizing
harmonic potential removes the periodicity of the optical lattice and leads to
localization. We also studied some dynamics of the localized state confirming
its stability
Matter-wave localization in a random potential
By numerical and variational solution of the Gross-Pitaevskii equation, we
studied the localization of a noninteracting and weakly-interacting
Bose-Einstein condensate (BEC) in a disordered cold atom lattice and a speckle
potential. In the case of a single BEC fragment, the variational analysis
produced good results. For a weakly disordered potential, the localized BECs
are found to have an exponential tail as in weak Anderson localization. We also
investigated the expansion of a noninteracting BEC in these potential. We find
that the BEC will be locked in an appropriate localized state after an initial
expansion and will execute breathing oscillation around a mean shape when a BEC
at equilibrium in a harmonic trap is suddenly released into a disorder
potential
Inverse Orbital Hall Effect Discovered from Light-Induced Terahertz Emission
Recent progress in orbitronics reveals the possibility of using orbital
current as an information carrier. The interconversion between orbital currents
and charge currents is crucial for orbital information processing. Although
orbital currents can be created from charge current via the orbital Hall
effect, the conversion from orbital current into charge current has not yet
been discovered experimentally, which is due to the lack of a reliable orbital
current source and disturbance of the omnipresent inverse spin Hall effect. In
this study, we generate ultrafast pulses of orbital current in magnetic
bilayers and trilayers from femtosecond laser pulses. We demonstrate that by
injecting orbital current pulses into nonmagnetic metals, the inverse orbital
Hall effect of the nonmagnetic layer induces a transient charge current and
emits terahertz electromagnetic pulses. The nonmagnetic metal layer acts as a
converter of the orbital current into the charge current. The discovery of the
inverse orbital Hall effect enables detection of orbital currents and opens a
new route for developing future orbitronic devices
DNA barcoding of Antarctic marine zooplankton for species identification and recognition
Polar zooplankton are particularly sensitive to climate change, and have been used as rapid-responders to indicate climate-induced changes in the fragile Antarctic ecosystem. DNA barcoding provides an alternative approach for rapid zooplankton species identification. Ninety-four specimens belonging to 32 Antarctic zooplankton species were barcoded to construct a comprehensive reference library. An 830 to 1 050 base-pair region of the mitochondrial cytochrome c oxidase subunit I (mtCOI) gene was obtained as DNA barcodes. The intraspecific variation of the gene ranged from 0 to 2.6% (p-distance), with an average of 0.67% (SD=0.67%). The distance between species within the same genera ranged from 0.1% (Calanus) to 29.3%, with an average of 15.3% (SD=8.4%). The morphological and genetic similarities between Calanus propinquus and C. simillimus raise new questions about the taxonomic status of C. simillimus. With the exception of the two Calanus species, the intraspecific genetic divergence was much smaller than the interspecific divergence among congeneric species, confirming the existence of a barcode gap for Antarctic zooplankton. In addition, species other than Calanus sp. formed a monophyletic group. Therefore, we have confirmed DNA barcoding as an accurate and efficient approach for zooplankton identification in the Antarctic area (except for Hydromedusa, Tunicata, and other gelatinous zooplankton). Indicator vector analysis further confirmed this conclusion. The new primer sets issued here may facilitate the study of Antarctic marine zooplankton species composition by environmental metagenetic analysis
Orbitronics: Light-induced Orbit Currents in Terahertz Emission Experiments
Orbitronics is based on the use of orbit currents as information carriers. Up
to now, orbit currents were created from the conversion of charge or spin
currents, and inversely, they could be converted back to charge or spin
currents. Here we demonstrate that orbit currents can also be generated by
femtosecond light pulses on Ni. In multilayers associating Ni with oxides and
nonmagnetic metals such as Cu, we detect the orbit currents by their conversion
into charge currents and the resulting terahertz emission. We show that the
orbit currents extraordinarily predominate the light-induced spin currents in
Ni-based systems, whereas only spin currents can be detected with CoFeB-based
systems. In addition, the analysis of the time delays of the terahertz pulses
leads to relevant information on the velocity and propagation of orbit
carriers. Our finding of light-induced orbit currents and our observation of
their conversion into charge currents opens new avenues in orbitronics,
including the development of orbitronic terahertz devices