453 research outputs found
Initializing an unmodulated spin chain to operate as a high quality quantum data-bus
We study the quality of state and entanglement transmission through quantum
channels described by spin chains varying both the system parameters and the
initial state of the channel. We consider a vast class of one-dimensional
many-body models which contains some of the most relevant experimental
realizations of quantum data-buses. In particular, we consider spin-1/2 XY and
XXZ model with open boundary conditions. Our results show a significant
difference between free-fermionic (non-interacting) systems (XY) and
interacting ones (XXZ), where in the former case initialization can be
exploited for improving the entanglement distribution, while in the latter case
it also determines the quality of state transmission. In fact, we find that in
non interacting systems the exchange with fermions in the initial state of the
chain always has a destructive effect, and we prove that it can be completely
removed in the isotropic XX model by initializing the chain in a ferromagnetic
state. On the other hand, in interacting systems constructive effects can arise
by scattering between hopping fermions and a proper initialization procedure.
Remarkably our results are the first example in which state and entanglement
transmission show maxima at different points as the interactions and
initializations of spin chain channels are varied.Comment: 10 pages, 7 figure
Low-control and robust quantum refrigerator and applications with electronic spins in diamond
We propose a general protocol for low-control refrigeration and thermometry
of thermal qubits, which can be implemented using electronic spins in diamond.
The refrigeration is implemented by a probe, consisting of a network of
interacting spins. The protocol involves two operations: (i) free evolution of
the probe; and (ii) a swap gate between one spin in the probe and the thermal
qubit we wish to cool. We show that if the initial state of the probe falls
within a suitable range, and the free evolution of the probe is both unital and
conserves the excitation in the -direction, then the cooling protocol will
always succeed, with an efficiency that depends on the rate of spin dephasing
and the swap gate fidelity. Furthermore, measuring the probe after it has
cooled many qubits provides an estimate of their temperature. We provide a
specific example where the probe is a Heisenberg spin chain, and suggest a
physical implementation using electronic spins in diamond. Here the probe is
constituted of nitrogen vacancy (NV) centers, while the thermal qubits are dark
spins. By using a novel pulse sequence, a chain of NV centers can be made to
evolve according to a Heisenberg Hamiltonian. This proposal allows for a range
of applications, such as NV-based nuclear magnetic resonance of photosensitive
molecules kept in a dark spot on a sample, and it opens up possibilities for
the study of quantum thermodynamics, environment-assisted sensing, and
many-body physics
Communication-Efficient Zeroth-Order Distributed Online Optimization: Algorithm, Theory, and Applications
This paper focuses on a multi-agent zeroth-order online optimization problem
in a federated learning setting for target tracking. The agents only sense
their current distances to their targets and aim to maintain a minimum safe
distance from each other to prevent collisions. The coordination among the
agents and dissemination of collision-prevention information is managed by a
central server using the federated learning paradigm. The proposed formulation
leads to an instance of distributed online nonconvex optimization problem that
is solved via a group of communication-constrained agents. To deal with the
communication limitations of the agents, an error feedback-based compression
scheme is utilized for agent-to-server communication. The proposed algorithm is
analyzed theoretically for the general class of distributed online nonconvex
optimization problems. We provide non-asymptotic convergence rates that show
the dominant term is independent of the characteristics of the compression
scheme. Our theoretical results feature a new approach that employs
significantly more relaxed assumptions in comparison to standard literature.
The performance of the proposed solution is further analyzed numerically in
terms of tracking errors and collisions between agents in two relevant
applications.Comment: 21 pages, 5 figures, and this paper has been accepted by IEEE Acces
The size-dependent electromechanical instability of double-sided and paddle-type actuators in centrifugal and Casimir force fields
The present research is devoted to theoretical study of the pull-in performance of double-sided and paddle-type NEMS actuators fabricated from cylindrical nanowire operating in the Casimir regime and in the presence of the centrifugal force. D'Alembert's principle was used to transform the angular velocity into an equivalent static, centrifugal force. Using the couple stress theory, the constitutive equations of the actuators were derived. The equivalent boundary condition technique was applied to obtain the governing equation of the paddle-type actuator. Three distinct approaches, the Duan-Adomian Method (DAM), Finite Difference Method (FDM), and Lumped Parameter Model (LPM), were applied to solve the equation of motion of these two actuators. This study demonstrates the influence of various parameters, i.e., the Casimir force, geometric characteristics, and the angular speed, on the pull-in performance. (C) 2017 Sharif University of Technology. All rights reserved
Statistical Mechanics of maximal independent sets
The graph theoretic concept of maximal independent set arises in several
practical problems in computer science as well as in game theory. A maximal
independent set is defined by the set of occupied nodes that satisfy some
packing and covering constraints. It is known that finding minimum and
maximum-density maximal independent sets are hard optimization problems. In
this paper, we use cavity method of statistical physics and Monte Carlo
simulations to study the corresponding constraint satisfaction problem on
random graphs. We obtain the entropy of maximal independent sets within the
replica symmetric and one-step replica symmetry breaking frameworks, shedding
light on the metric structure of the landscape of solutions and suggesting a
class of possible algorithms. This is of particular relevance for the
application to the study of strategic interactions in social and economic
networks, where maximal independent sets correspond to pure Nash equilibria of
a graphical game of public goods allocation
Preliminary Evidence of Acceptance and Commitment Therapy for Death Anxiety in Iranian Clients Diagnosed with OCD
This study investigated the effectiveness of Acceptance and Commitment Therapy (ACT) on death anxiety and obsessive-compulsive disorder (OCD) with eight adult females in Iran. The ACT protocol was conducted in 8 weekly solo sessions (45 minutes each). The results were analyzed by visual analysis method and improvement percentage. ACT resulted in decreases in death anxiety (60-80%) and obsessive-compulsive symptoms (51-60%), thereby indicating promise for ACT as a treatment for OCD and death anxiety
In vivo regulation of the heme oxygenase-1 gene in humanized transgenic mice
Heme oxygenase-1 (HO-1) catalyzes the rate-limiting step in heme degradation, producing equimolar amounts of carbon monoxide, iron, and biliverdin. Induction of HO-1 is a beneficial response to tissue injury in diverse animal models of diseases including acute kidney injury. In vitro analysis has shown that the human HO-1 gene is transcriptionally regulated by changes in chromatin conformation, but whether such control occurs in vivo is not known. To enable such an analysis, we generated transgenic mice, harboring an 87-kb bacterial artificial chromosome expressing human HO-1 mRNA and protein and bred these mice with HO-1 knockout mice to generate humanized BAC transgenic mice. This successfully rescued the phenotype of the knockout mice including reduced birth rates, tissue iron overload, splenomegaly, anemia, leukocytosis, dendritic cell abnormalities, and survival after acute kidney injury induced by rhabdomyolysis or cisplatin nephrotoxicity. Transcription factors such as USF1/2, JunB, Sp1, and CTCF were found to associate with regulatory regions of the human HO-1 gene in the kidney following rhabdomyolysis. Chromosome conformation capture and ChIP-loop assays confirmed this in the formation of chromatin looping in vivo. Thus, these bacterial artificial chromosome humanized HO-1 mice are a valuable model to study the human HO-1 gene, providing insight to the in vivo architecture of the gene in acute kidney injury and other diseases
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