120 research outputs found
Dynamics of entanglement of bosonic modes on symmetric graphs
We investigate the dynamics of an initially disentangled Gaussian state on a
general finite symmetric graph. As concrete examples we obtain properties of
this dynamics on mean field graphs of arbitrary sizes. In the same way that
chains can be used for transmitting entanglement by their natural dynamics,
these graphs can be used to store entanglement. We also consider two kinds of
regular polyhedron which show interesting features of entanglement sharing.Comment: 14 pages, 11 figures, Accepted for publication in Physics Letters
Interaction Driven Quantum Hall Wedding cake-like Structures in Graphene Quantum Dots
Quantum-relativistic matter is ubiquitous in nature; however it is
notoriously difficult to probe. The ease with which external electric and
magnetic fields can be introduced in graphene opens a door to creating a
table-top prototype of strongly confined relativistic matter. Here, through a
detailed spectroscopic mapping, we provide a spatial visualization of the
interplay between spatial and magnetic confinement in a circular graphene
resonator. We directly observe the development of a multi-tiered "wedding
cake"-like structure of concentric regions of compressible/incompressible
quantum Hall states, a signature of electron interactions in the system.
Solid-state experiments can therefore yield insights into the behaviour of
quantum-relativistic matter under extreme conditions
Occupational challenges in the caregivers of people with multiple sclerosis: A qualitative study
Background: Multiple Sclerosis (MS) is a neurodegenerative disorder. The progressive and unpredictable nature of MS indicates the patients� need for long-term care as well as the increased burden of their primary caregivers� care and occupational challenges that emerge in their daily life activities. Objectives: The current study aimed to explore the occupational challenges caused by engaging in the care process for the caregivers of people with MS Methods: This qualitative study was conducted on 21 caregivers of MS patients using a content analysis approach. Data were collected through semi-structured face-to-face interviews. Results: Three main themes emerged: Time limitations in occupation implementation, care needs in occupation implementation, and emotional reactions affecting occupations. Conclusions: According to the results, the caregivers of people with MS were faced with a variety of occupational challenges. The time limitations for performing routine occupations and desired activities, unmet patient care-facilitating needs, and the occurrence of psychosocial reactions and behaviors were contributed to these challenges and their exacerbation. Identifying these challenges is both useful for designing interventional programs and to help caregivers to successfully perform their desired occupations in spite of challenges in the care process. © 2020, Semnan University of Medical Sciences. All rights reserved
Interaction-driven quantum Hall wedding cake–like structures in graphene quantum dots
Quantum-relativistic matter is ubiquitous in nature; however, it is notoriously difficult to probe. The ease with which external electric and magnetic fields can be introduced in graphene opens a door to creating a tabletop prototype of strongly confined relativistic matter. Here, through a detailed spectroscopic mapping, we directly visualize the interplay between spatial and magnetic confinement in a circular graphene resonator as atomic-like shell states condense into Landau levels. We directly observe the development of a “wedding cake”–like structure of concentric regions of compressible-incompressible quantum Hall states, a signature of electron interactions in the system. Solid-state experiments can, therefore, yield insights into the behavior of quantum-relativistic matter under extreme conditions.United States. National Science Foundation. STC Center for Integrated Quantum Materials (Award 1231319)United States. Army Research Office. Institute for Soldier Nanotechnologies (Contract W911NF-13-D-0001
Multicomponent fractional quantum Hall effect in graphene
We report observation of the fractional quantum Hall effect (FQHE) in high
mobility multi-terminal graphene devices, fabricated on a single crystal boron
nitride substrate. We observe an unexpected hierarchy in the emergent FQHE
states that may be explained by strongly interacting composite Fermions with
full SU(4) symmetric underlying degrees of freedom. The FQHE gaps are measured
from temperature dependent transport to be up 10 times larger than in any other
semiconductor system. The remarkable strength and unusual hierarcy of the FQHE
described here provides a unique opportunity to probe correlated behavior in
the presence of expanded quantum degrees of freedom.Comment: 5 pages, 3 figure
Erratum to: Providing Patients with Implantable Cardiac Device Data through a Personal Health Record: A Qualitative Study
Erratum to: Providing Patients with Implantable Cardiac Device Data through a Personal Health Record: A Qualitative Study. [Appl Clin Inform. 2017
Tuning a Circular p-n Junction in Graphene from Quantum Confinement to Optical Guiding
The motion of massless Dirac-electrons in graphene mimics the propagation of
photons. This makes it possible to control the charge-carriers with components
based on geometrical-optics and has led to proposals for an all-graphene
electron-optics platform. An open question arising from the possibility of
reducing the component-size to the nanometer-scale is how to access and
understand the transition from optical-transport to quantum-confinement. Here
we report on the realization of a circular p-n junction that can be
continuously tuned from the nanometer-scale, where quantum effects are
dominant, to the micrometer scale where optical-guiding takes over. We find
that in the nanometer-scale junction electrons are trapped in states that
resemble atomic-collapse at a supercritical charge. As the junction-size
increases, the transition to optical-guiding is signaled by the emergence of
whispering-gallery modes and Fabry-Perot interference. The creation of tunable
junctions that straddle the crossover between quantum-confinement and
optical-guiding, paves the way to novel design-architectures for controlling
electronic transport.Comment: 16 pages, 4 figure
An On/Off Berry Phase Switch in Circular Graphene Resonators
The phase of a quantum state may not return to its original value after the
system's parameters cycle around a closed path; instead, the wavefunction may
acquire a measurable phase difference called the Berry phase. Berry phases
typically have been accessed through interference experiments. Here, we
demonstrate an unusual Berry-phase-induced spectroscopic feature: a sudden and
large increase in the energy of angular-momentum states in circular graphene
p-n junction resonators when a small critical magnetic field is reached. This
behavior results from turning on a -Berry phase associated with the
topological properties of Dirac fermions in graphene. The Berry phase can be
switched on and off with small magnetic field changes on the order of 10 mT,
potentially enabling a variety of optoelectronic graphene device applications
Magnetic Catalysis and Quantum Hall Ferromagnetism in Weakly Coupled Graphene
We study the realization in a model of graphene of the phenomenon whereby the
tendency of gauge-field mediated interactions to break chiral symmetry
spontaneously is greatly enhanced in an external magnetic field. We prove that,
in the weak coupling limit, and where the electron-electron interaction
satisfies certain mild conditions, the ground state of charge neutral graphene
in an external magnetic field is a quantum Hall ferromagnet which spontaneously
breaks the emergent U(4) symmetry to U(2)XU(2).
We argue that, due to a residual CP symmetry, the quantum Hall ferromagnet
order parameter is given exactly by the leading order in perturbation theory.
On the other hand, the chiral condensate which is the order parameter for
chiral symmetry breaking generically obtains contributions at all orders. We
compute the leading correction to the chiral condensate. We argue that the
ensuing fermion spectrum resembles that of massive fermions with a vanishing
U(4)-valued chemical potential. We discuss the realization of parity and charge
conjugation symmetries and argue that, in the context of our model, the charge
neutral quantum Hall state in graphene is a bulk insulator, with vanishing
longitudinal conductivity due to a charge gap and Hall conductivity vanishing
due to a residual discrete particle-hole symmetry.Comment: 35 page
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