26 research outputs found
Topological lattice using multi-frequency radiation
We describe a novel technique for creating an artificial magnetic field for
ultra-cold atoms using a periodically pulsed pair of counter propagating Raman
lasers that drive transitions between a pair of internal atomic spin states: a
multi-frequency coupling term. In conjunction with a magnetic field gradient,
this dynamically generates a rectangular lattice with a non-staggered magnetic
flux. For a wide range of parameters, the resulting Bloch bands have
non-trivial topology, reminiscent of Landau levels, as quantified by their
Chern numbers.Comment: Replaced with a revised version, 15 pages, 6 figure
Weak-Measurement-Induced Heating in Bose-Einstein Condensates
Ultracold atoms are an ideal platform for understanding system-reservoir
dynamics of many-body systems. Here, we study quantum back-action in atomic
Bose-Einstein condensates, weakly interacting with a far-from resonant, i.e.,
dispersively interacting, probe laser beam. The light scattered by the atoms
can be considered as a part of quantum measurement process whereby the change
in the system state derives from measurement back-action. We experimentally
quantify the resulting back-action in terms of the deposited energy. We model
the interaction of the system and environment with a generalized measurement
process, leading to a Markovian reservoir. Further, we identify two systematic
sources of heating and loss: a stray optical lattice and probe-induced light
assisted collisions (an intrinsic atomic process). The observed heating and
loss rates are larger for blue detuning than for red detuning, where they are
oscillatory functions of detuning with increased loss at molecular resonances
and reduced loss between molecular resonances.Comment: 13 pages, 8 figures. arXiv admin note: text overlap with
arXiv:2209.0440
Realistic Rashba and Dressehaus spin-orbit coupling for neutral atoms
We describe a new class of atom-laser coupling schemes which lead to
spin-orbit coupled Hamiltonians for ultra-cold neutral atoms. By properly
setting the optical phases, a pair of degenerate pseudospin states emerge as
the lowest energy states in the spectrum, and are thus immune to collisionally
induced decay. These schemes use cyclically coupled ground or metastable
internal states. We specialize to two situations: a three level case giving
fixed Rashba coupling, and a four-level case that adds a controllable
Dresselhaus contribution. We describe an implementation of the four level
scheme for \Rb87 and analyze the sensitivity of our approach to realistic
experimental limitations and imperfections. Lastly, we argue that no laser
coupling scheme can give pure Rashba or Dresselhaus coupling: akin to condensed
matter systems, higher order terms spoil the symmetry of these couplings.
However, for sufficiently intense laser fields the continuous rotational
symmetry approximately holds, making the Rashba Hamiltonian applicable for cold
atoms.Comment: 5 pages, 4 figures, accepted as a PRA Brief Repor
Repeated Measurements with Minimally Destructive Partial-Transfer Absorption Imaging
We demonstrate partial-transfer absorption imaging as a technique for
repeatedly imaging an ultracold atomic ensemble with minimal perturbation. We
prepare an atomic cloud in a state that is dark to the imaging light. We then
use a microwave pulse to coherently transfer a small fraction of the ensemble
to a bright state, which we image using in situ absorption imaging. The
amplitude or duration of the microwave pulse controls the fractional transfer
from the dark to the bright state. For small transfer fractions, we can image
the atomic cloud up to 50 times before it is depleted. As a sample application,
we repeatedly image an atomic cloud oscillating in a dipole trap to measure the
trap frequency.Comment: 12 pages, 7 figure
Tunneling in the topological mechanism of superconductivity
We compute the two-particle matrix element and Josephson tunneling amplitude
in a two-dimensional model of topological superconductivity which captures the
physics of the doped Mott insulator. The hydrodynamics of topological
electronic liquid consists of the compressible charge sector and the
incompressible chiral topological spin liquid. We show that ground states
differing by an odd number of particles are orthogonal and insertion of two
extra electrons is followed by the emission of soft modes of the transversal
spin current. The orthogonality catastrophe makes the physics of
superconductivity drastically different from the BCS-theory but similar to the
physics of one-dimensional electronic liquids. The wave function of a pair is
dressed by soft modes. As a result the two particle matrix element forms a
complex d-wave representation (i.e., changes sign under degree
rotation), although the gap in the electronic spectrum has no nodes. In
contrast to the BCS-theory the tunneling amplitude has an asymmetric broad peak
(much bigger than the gap) around the Fermi surface. We develop an operator
algebra, that allows one to compute other correlation functions.Comment: 18 pages, 2 eps figures, revtex, psfig, significant changes have been
mad
Identification, Replication, and Functional Fine-Mapping of Expression Quantitative Trait Loci in Primary Human Liver Tissue
The discovery of expression quantitative trait loci (“eQTLs”) can
help to unravel genetic contributions to complex traits. We identified genetic
determinants of human liver gene expression variation using two independent
collections of primary tissue profiled with Agilent
(n = 206) and Illumina (n = 60)
expression arrays and Illumina SNP genotyping (550K), and we also incorporated
data from a published study (n = 266). We found that
∼30% of SNP-expression correlations in one study failed to replicate
in either of the others, even at thresholds yielding high reproducibility in
simulations, and we quantified numerous factors affecting reproducibility. Our
data suggest that drug exposure, clinical descriptors, and unknown factors
associated with tissue ascertainment and analysis have substantial effects on
gene expression and that controlling for hidden confounding variables
significantly increases replication rate. Furthermore, we found that
reproducible eQTL SNPs were heavily enriched near gene starts and ends, and
subsequently resequenced the promoters and 3′UTRs for 14 genes and tested
the identified haplotypes using luciferase assays. For three genes, significant
haplotype-specific in vitro functional differences correlated
directly with expression levels, suggesting that many bona fide
eQTLs result from functional variants that can be mechanistically isolated in a
high-throughput fashion. Finally, given our study design, we were able to
discover and validate hundreds of liver eQTLs. Many of these relate directly to
complex traits for which liver-specific analyses are likely to be relevant, and
we identified dozens of potential connections with disease-associated loci.
These included previously characterized eQTL contributors to diabetes, drug
response, and lipid levels, and they suggest novel candidates such as a role for
NOD2 expression in leprosy risk and
C2orf43 in prostate cancer. In general, the work presented
here will be valuable for future efforts to precisely identify and functionally
characterize genetic contributions to a variety of complex traits