345 research outputs found
Schwinger pair production with ultracold atoms
We consider a system of ultracold atoms in an optical lattice as a quantum
simulator for electron-positron pair production in quantum electrodynamics
(QED). For a setup in one spatial dimension, we investigate the nonequilibrium
phenomenon of pair production including the backreaction leading to plasma
oscillations. Unlike previous investigations on quantum link models, we focus
on the infinite-dimensional Hilbert space of QED and show that it may be well
approximated by experiments employing Bose-Einstein condensates interacting
with fermionic atoms. The calculations based on functional integral techniques
give a unique access to the physical parameters required to realize the QED
phenomena in a cold atom experiment. In particular, we use our approach to
consider quantum link models in a yet unexplored parameter regime and give
bounds for their ability to capture essential features of the physics. The
results suggest a paradigmatic change towards realizations using coherent
many-body states rather than single atoms for quantum simulations of
high-energy particle physics phenomena.Comment: 5 pages, 4 figures, PLB versio
Tying Together the Tax and Bankruptcy Codes: What Is the Proper Tax Treatment of Abandonments in Bankruptcy?
Momentum Spectra for Dynamically Assisted Schwinger Pair Production
Recently the dynamically assisted Schwinger mechanism, i.e.,
electron-positron pair production from vacuum by a combination of laser pulses
with different time scales has been proposed. The corresponding results, which
suggest that the rate of produced pairs is significantly enhanced by dynamical
effects, are verified. Employing the framework of quantum kinetic theory
intrinsically enables us to additionally provide momentum space information on
the generated positron spectrum.Comment: 6 pages, 7 figure
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
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
Molecular and immunological characterization of profilin from mugwort pollen
In late summer in Europe, pollen of mugwort is one of the major sources of atopic allergens. No information about the complete molecular structure of any mugwort allergen has been published so far. Here we report the isolation and characterization of mugwort pollen cDNA clones coding for two isoforms of the panallergen profilin. Thirtysix percent of the mugwort allergic patients tested displayed IgE antibodies against natural and recombinant profilin, and no significant differences were observed in the IgEbinding properties of the isoforms. One profilin isoform was purified to homogeneity and detailed structural analysis indicated that the protein exists in solution as dimers and tetramers stabilized by sulfydryl and/or ionic interactions. Profilin monomers were detectable only after exposure of multimers to harsh denaturing conditions. Dimers and tetramers did not significantly differ in their ability to bind serum IgE from mugwort pollenallergic patients. However, oligomeric forms might have a higher allergenic potential than monomers because larger molecules would have additional epitopes for IgEmediated histamine release. Profilin isolated from mugwort pollen also formed multimers. Thus, oligomerization is not an artifact resulting from the recombinant production of the allergen. Inhibition experiments showed extensive IgE crossreactivity of recombinant mugwort profilin and profilin from various pollen and food extracts
Symmetries and local transformations of translationally invariant Matrix Product States
We determine the local symmetries and local transformation properties of
translationally invariant matrix product states (MPS). We focus on physical
dimension and bond dimension and use the procedure introduced in D.
Sauerwein et al., Phys. Rev. Lett. 123, 170504 (2019) to determine all
(including non--global) symmetries of those states. We identify and classify
the stochastic local transformations (SLOCC) that are allowed among MPS. We
scrutinize two very distinct sets of MPS and show the big diversity (also
compared to the case ) occurring in both, their symmetries and the
possible SLOCC transformations. These results reflect the variety of local
properties of MPS, even if restricted to translationally invariant states with
low bond dimension. Finally, we show that states with non-trivial local
symmetries are of measure zero for and .Comment: 40 pages, 5 figure
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