94 research outputs found
Implementing quantum electrodynamics with ultracold atomic systems
We discuss the experimental engineering of model systems for the description
of QED in one spatial dimension via a mixture of bosonic Na and
fermionic Li atoms. The local gauge symmetry is realized in an optical
superlattice, using heteronuclear boson-fermion spin-changing interactions
which preserve the total spin in every local collision. We consider a large
number of bosons residing in the coherent state of a Bose-Einstein condensate
on each link between the fermion lattice sites, such that the behavior of
lattice QED in the continuum limit can be recovered. The discussion about the
range of possible experimental parameters builds, in particular, upon
experiences with related setups of fermions interacting with coherent samples
of bosonic atoms. We determine the atomic system's parameters required for the
description of fundamental QED processes, such as Schwinger pair production and
string breaking. This is achieved by benchmark calculations of the atomic
system and of QED itself using functional integral techniques. Our results
demonstrate that the dynamics of one-dimensional QED may be realized with
ultracold atoms using state-of-the-art experimental resources. The experimental
setup proposed may provide a unique access to longstanding open questions for
which classical computational methods are no longer applicable
Observation of the phononic Lamb shift with a synthetic vacuum
The quantum vacuum fundamentally alters the properties of embedded particles.
In contrast to classical empty space, it allows for creation and annihilation
of excitations. For trapped particles this leads to a change in the energy
spectrum, known as Lamb shift. Here, we engineer a synthetic vacuum building on
the unique properties of ultracold atomic gas mixtures. This system makes it
possible to combine high-precision spectroscopy with the ability of switching
between empty space and quantum vacuum. We observe the phononic Lamb shift, an
intruiguing many-body effect orginally conjectured in the context of solid
state physics. Our study therefore opens up new avenues for high-precision
benchmarking of non-trivial theoretical predictions in the realm of the quantum
vacuum
Quantum simulation of lattice gauge theories using Wilson fermions
Quantum simulators have the exciting prospect of giving access to real-time
dynamics of lattice gauge theories, in particular in regimes that are difficult
to compute on classical computers. Future progress towards scalable quantum
simulation of lattice gauge theories, however, hinges crucially on the
efficient use of experimental resources. As we argue in this work, due to the
fundamental non-uniqueness of discretizing the relativistic Dirac Hamiltonian,
the lattice representation of gauge theories allows for an optimization that up
to now has been left unexplored. We exemplify our discussion with lattice
quantum electrodynamics in two-dimensional space-time, where we show that the
formulation through Wilson fermions provides several advantages over the
previously considered staggered fermions. Notably, it enables a strongly
simplified optical lattice setup and it reduces the number of degrees of
freedom required to simulate dynamical gauge fields. Exploiting the optimal
representation, we propose an experiment based on a mixture of ultracold atoms
trapped in a tilted optical lattice. Using numerical benchmark simulations, we
demonstrate that a state-of-the-art quantum simulator may access the Schwinger
mechanism and map out its non-perturbative onset.Comment: 19 pages, 11 figure
Resistive flow in a weakly interacting Bose-Einstein condensate
We report the direct observation of resistive flow through a weak link in a
weakly interacting atomic Bose-Einstein condensate. Two weak links separate our
ring-shaped superfluid atomtronic circuit into two distinct regions, a source
and a drain. Motion of these weak links allows for creation of controlled flow
between the source and the drain. At a critical value of the weak link
velocity, we observe a transition from superfluid flow to superfluid plus
resistive flow. Working in the hydrodynamic limit, we observe a conductivity
that is 4 orders of magnitude larger than previously reported conductivities
for a Bose-Einstein condensate with a tunnel junction. Good agreement with
zero-temperature Gross-Pitaevskii simulations and a phenomenological model
based on phase slips indicate that the creation of excitations plays an
important role in the resulting conductivity. Our measurements of resistive
flow elucidate the microscopic origin of the dissipation and pave the way for
more complex atomtronic devices.Comment: Version published in PR
Interferometric measurement of the current-phase relationship of a superfluid weak link
Weak connections between superconductors or superfluids can differ from
classical links due to quantum coherence, which allows flow without resistance.
Transport properties through such weak links can be described with a single
function, the current-phase relationship, which serves as the quantum analog of
the current-voltage relationship. Here, we present a technique for
inteferometrically measuring the current-phase relationship of superfluid weak
links. We interferometrically measure the phase gradient around a ring-shaped
superfluid Bose-Einstein condensate (BEC) containing a rotating weak link,
allowing us to identify the current flowing around the ring. While our BEC weak
link operates in the hydrodynamic regime, this technique can be extended to all
types of weak links (including tunnel junctions) in any phase-coherent quantum
gas. Moreover, it can also measure the current-phase relationships of
excitations. Such measurements may open new avenues of research in quantum
transport.Comment: 6 pages, 4 figures. Contact S. Eckel (below) for supplemental
informatio
Clinical implications of GWAS variants associated with differentiated thyroid cancer
The genetic risk of differentiated thyroid cancer (DTC) probably consists of multiple low-penetrance, single-nucleotide polymorphisms (SNP). Such markers are difficult to uncover by linkage analysis but can be revealed by association studies. Genome-wide association studies (GWASs) have uncovered 31 SNPs associated with DTC. These markers carry a low to moderate risk for DTC, but their cumulative effect increases with each successive risk allele. These data support the important contribution of low penetrance variants in the pathogenesis of DTC. Contrary to somatic mutations such as BRAFV600E, germline variants can be ascertained prior to surgical treatment. Therefore, we hypothesise that GWAS SNPs might impact the clinical course of DTC and we can benefit from this knowledge in choosing a treatment strategy. Several associations between clinical factors and GWAS markers have been reported so far. The most important are associations between rs966423 and mortality (HR = 1.60, p = 0.038), extrathyroidal extension (ETE) (OR = 1.57, p = 0.019); rs965513 and tumour diameter (slope of regression 0.14, p = 0.025), lymph node metastasis (OR = 1.59, p = 0.030) and ETE (OR = 1.29, p = 0.045); rs944289 and distant metastasis (OR = 0.58, p = 0.042); and rs116909374 and lymph node metastasis (OR = 0.61, p = 0.016). These findings show that GWAS SNPs are not only the ignition factors (together with environmental factors) for malignant transformation of thyrocytes but might also impact the clinical course of DTC. Surprisingly, it is not always the risk allele for DTC that is associated with worse clinical outcome. The second interesting observation is that GWAS SNPs show different associations with DTC clinical features depending on their histological subtypes. These point to the complexity of DTC with putatively different roles of genes at different stages of DTC development. (Endokrynol Pol 2019; 70 (5): 423–429
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