1,854 research outputs found
Superfluid and magnetic states of an ultracold Bose gas with synthetic three-dimensional spin-orbit coupling in an optical lattice
We study ultracold bosonic atoms with the synthetic three-dimensional
spin-orbit (SO) coupling in a cubic optical lattice. In the superfluidity
phase, the lowest energy band exhibits one, two or four pairs of degenerate
single-particle ground states depending on the SO-coupling strengths, which can
give rise to the condensate states with spin-stripes for the weak atomic
interactions. In the deep Mott-insulator regime, the effective spin Hamiltonian
of the system combines three-dimensional Heisenberg exchange interactions,
anisotropy interactions and Dzyaloshinskii-Moriya interactions. Based on Monte
Carlo simulations, we numerically demonstrate that the resulting Hamiltonian
with an additional Zeeman field has a rich phase diagram with spiral, stripe,
vortex crystal, and especially Skyrmion crystal spin-textures in each xy-plane
layer. The obtained Skyrmion crystals can be tunable with square and hexagonal
symmetries in a columnar manner along the z axis, and moreover are stable
against the inter-layer spin-spin interactions in a large parameter region.Comment: 9 pages, 4 figures; title modified, references and discussions added;
accepted by PR
Valley-dependent gauge fields for ultracold atoms in square optical superlattices
We propose an experimental scheme to realize the valley-dependent gauge
fields for ultracold fermionic atoms trapped in a state-dependent square
optical lattice. Our scheme relies on two sets of Raman laser beams to engineer
the hopping between adjacent sites populated by two-component fermionic atoms.
One set of Raman beams are used to realize a staggered \pi-flux lattice, where
low energy atoms near two inequivalent Dirac points should be described by the
Dirac equation for spin-1/2 particles. Another set of laser beams with proper
Rabi frequencies are added to further modulate the atomic hopping parameters.
The hopping modulation will give rise to effective gauge potentials with
opposite signs near the two valleys, mimicking the interesting strain-induced
pseudo-gauge fields in graphene. The proposed valley-dependent gauge fields are
tunable and provide a new route to realize quantum valley Hall effects and
atomic valleytronics.Comment: 5+ pages, 2 figures; language polished, references and discussions
added; accepted by PR
PseudoCal: A Source-Free Approach to Unsupervised Uncertainty Calibration in Domain Adaptation
Unsupervised domain adaptation (UDA) has witnessed remarkable advancements in
improving the accuracy of models for unlabeled target domains. However, the
calibration of predictive uncertainty in the target domain, a crucial aspect of
the safe deployment of UDA models, has received limited attention. The
conventional in-domain calibration method, \textit{temperature scaling}
(TempScal), encounters challenges due to domain distribution shifts and the
absence of labeled target domain data. Recent approaches have employed
importance-weighting techniques to estimate the target-optimal temperature
based on re-weighted labeled source data. Nonetheless, these methods require
source data and suffer from unreliable density estimates under severe domain
shifts, rendering them unsuitable for source-free UDA settings. To overcome
these limitations, we propose PseudoCal, a source-free calibration method that
exclusively relies on unlabeled target data. Unlike previous approaches that
treat UDA calibration as a \textit{covariate shift} problem, we consider it as
an unsupervised calibration problem specific to the target domain. Motivated by
the factorization of the negative log-likelihood (NLL) objective in TempScal,
we generate a labeled pseudo-target set that captures the structure of the real
target. By doing so, we transform the unsupervised calibration problem into a
supervised one, enabling us to effectively address it using widely-used
in-domain methods like TempScal. Finally, we thoroughly evaluate the
calibration performance of PseudoCal by conducting extensive experiments on 10
UDA methods, considering both traditional UDA settings and recent source-free
UDA scenarios. The experimental results consistently demonstrate the superior
performance of PseudoCal, exhibiting significantly reduced calibration error
compared to existing calibration methods
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Evaluation of five satellite top-of-atmosphere albedo products over land
Five satellite top-of-atmosphere (TOA) albedo products over land were evaluated in this study including global products from the Advanced Very High Resolution Radiometer (AVHRR) (TAL-AVHRR), Moderate Resolution Imaging Spectroradiometer (MODIS) (TAL-MODIS), and Clouds and the Earth’s Radiant Energy System (CERES); one regional product from the Climate Monitoring Satellite Application Facility (CM SAF); and one harmonized product termed Diagnosing Earth’s Energy Pathways in the Climate system (DEEP-C). Results showed that overall, there is good consistency among these five products, particularly after the year 2000. The differences among these products in the high-latitude regions were relatively larger. The percentage differences among TAL-AVHRR, TAL-MODIS, and CERES were generally less than 20%, while the differences between TAL-AVHRR and DEEP-C before 2000 were much larger. Except for the obvious decrease in the differences after 2000, the differences did not show significant changes over time, but varied among different regions. The differences between TAL-AVHRR and the other products were relatively large in the high-latitude regions of North America, Asia, and the Maritime Continent, while the differences between DEEP-C and CM SAF in Europe and Africa were smaller. Interannual variability was consistent between products after 2000, before which the differences among the three products were much larger
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