5,451 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
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
5G Wireless Network Slicing for eMBB, URLLC, and mMTC: A Communication-Theoretic View
The grand objective of 5G wireless technology is to support three generic
services with vastly heterogeneous requirements: enhanced mobile broadband
(eMBB), massive machine-type communications (mMTC), and ultra-reliable
low-latency communications (URLLC). Service heterogeneity can be accommodated
by network slicing, through which each service is allocated resources to
provide performance guarantees and isolation from the other services. Slicing
of the Radio Access Network (RAN) is typically done by means of orthogonal
resource allocation among the services. This work studies the potential
advantages of allowing for non-orthogonal sharing of RAN resources in uplink
communications from a set of eMBB, mMTC and URLLC devices to a common base
station. The approach is referred to as Heterogeneous Non-Orthogonal Multiple
Access (H-NOMA), in contrast to the conventional NOMA techniques that involve
users with homogeneous requirements and hence can be investigated through a
standard multiple access channel. The study devises a communication-theoretic
model that accounts for the heterogeneous requirements and characteristics of
the three services. The concept of reliability diversity is introduced as a
design principle that leverages the different reliability requirements across
the services in order to ensure performance guarantees with non-orthogonal RAN
slicing. This study reveals that H-NOMA can lead, in some regimes, to
significant gains in terms of performance trade-offs among the three generic
services as compared to orthogonal slicing.Comment: Submitted to IEE
Medical Comorbidities of Dementia: Links to Caregiversâ Emotional Difficulties and Gains
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154268/1/jgs16244_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154268/2/jgs16244.pd
How Glutamate Receptor Subunits Mix and Match: Details Uncovered
Until now, the atomic details explaining why certain subunits prefer to coassemble has been lacking in our understanding of glutamate receptor biogenesis. In this issue, Kumar et al. describe the structural basis by which preferential subunit assembly occurs for homomeric and heteromeric kainate-type glutamate receptors
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