85 research outputs found
Approaching the Ground State of a Quantum Spin Glass using a Zero-Temperature Quantum Monte Carlo
Here we discuss the annealing behavior of an infinite-range Ising
spin glass in presence of a transverse field using a zero-temperature quantum
Monte Carlo. Within the simulation scheme, we demonstrate that quantum
annealing not only helps finding the ground state of a classical spin glass,
but can also help simulating the ground state of a quantum spin glass, in
particularly, when the transverse field is low, much more efficiently.Comment: 8 pages, 6 fig
Quantum Annealing in a Kinetically Constrained System
Classical and quantum annealing is discussed for a kinetically constrained
chain of non-interacting asymmetric double wells, represented by Ising
spins in a longitudinal field . It is shown that in certain cases, where the
kinetic constraints may arise from infinitely high but vanishingly narrow
barriers appearing in the relaxation path of the system, quantum annealing
exploiting the quantum-mechanical penetration of sufficiently narrow barriers
may be far more efficient than its thermal counterpart.
We have used a semiclassical picture of scattering dynamics to do our
simulation for the quantum system.Comment: 5 pages, 3 figure
How should you evaluate elevated calcium in an asymptomatic patient?
Patients with unexplained asymptomatic true hypercalcemia should be screened for primary hyperparathyroidism (PHPT) and malignancy using an intact parathyroid hormone (PTH) level by immunoradioassay (SOR: C, expert opinion). Other recommended tests that can distinguish PHPT from malignancy and familial hypocalciuric hypercalcemia, as well as help manage patients with PHPT include urinary 24-hour calcium and creatinine levels, parathyroid hormone related peptide (PTHrP), alkaline phosphatase, calcitriol, and bone densitometry (SOR: C, expert opinion)
A scaling theory of quantum breakdown in solids
We propose a new scaling theory for general quantum breakdown phenomena. We
show, taking Landau-Zener type breakdown as a particular example, that the
breakdown phenomena can be viewed as a quantum phase transition for which the
scaling theory is developed. The application of this new scaling theory to
Zener type breakdown in Anderson insulators, and quantum quenching has been
discussed.Comment: 3 page
Continuous transition of social efficiencies in the stochastic strategy Minority Game
We show that in a variant of the Minority Game problem, the agents can reach
a state of maximum social efficiency, where the fluctuation between the two
choices is minimum, by following a simple stochastic strategy. By imagining a
social scenario where the agents can only guess about the number of excess
people in the majority, we show that as long as the guess value is sufficiently
close to the reality, the system can reach a state of full efficiency or
minimum fluctuation. A continuous transition to less efficient condition is
observed when the guess value becomes worse. Hence, people can optimize their
guess value for excess population to optimize the period of being in the
majority state. We also consider the situation where a finite fraction of
agents always decide completely randomly (random trader) as opposed to the rest
of the population that follow a certain strategy (chartist). For a single
random trader the system becomes fully efficient with majority-minority
crossover occurring every two-days interval on average. For just two random
traders, all the agents have equal gain with arbitrarily small fluctuations.Comment: 8 pages, 6 fig
Infinite-range Ising ferromagnet in a time-dependent transverse field: quench and ac dynamics near the quantum critical point
We study an infinite range ferromagnetic Ising model in the presence of a
transverse magnetic field which exhibits a quantum paramagnetic-ferromagnetic
phase transition at a critical value of the transverse field. In the
thermodynamic limit, the low-temperature properties of this model are dominated
by the behavior of a single large classical spin governed by an anisotropic
Hamiltonian. Using this property, we study the quench and AC dynamics of the
model both numerically and analytically, and develop a correspondence between
the classical phase space dynamics of a single spin and the quantum dynamics of
the infinite-range ferromagnetic Ising model. In particular, we compare the
behavior of the equal-time order parameter correlation function both near to
and away from the quantum critical point in the presence of a quench or AC
transverse field. We explicitly demonstrate that a clear signature of the
quantum critical point can be obtained by studying the AC dynamics of the
system even in the classical limit. We discuss possible realizations of our
model in experimental systems.Comment: Revtex4, 10 pages including 10 figures; corrected a sign error in Eq.
32; this is the final published versio
Quantum Annealing and Analog Quantum Computation
We review here the recent success in quantum annealing, i.e., optimization of
the cost or energy functions of complex systems utilizing quantum fluctuations.
The concept is introduced in successive steps through the studies of mapping of
such computationally hard problems to the classical spin glass problems. The
quantum spin glass problems arise with the introduction of quantum
fluctuations, and the annealing behavior of the systems as these fluctuations
are reduced slowly to zero. This provides a general framework for realizing
analog quantum computation.Comment: 22 pages, 7 figs (color online); new References Added. Reviews of
Modern Physics (in press
Failure Processes in Elastic Fiber Bundles
The fiber bundle model describes a collection of elastic fibers under load.
the fibers fail successively and for each failure, the load distribution among
the surviving fibers change. Even though very simple, the model captures the
essentials of failure processes in a large number of materials and settings. We
present here a review of fiber bundle model with different load redistribution
mechanism from the point of view of statistics and statistical physics rather
than materials science, with a focus on concepts such as criticality,
universality and fluctuations. We discuss the fiber bundle model as a tool for
understanding phenomena such as creep, and fatigue, how it is used to describe
the behavior of fiber reinforced composites as well as modelling e.g. network
failure, traffic jams and earthquake dynamics.Comment: This article has been Editorially approved for publication in Reviews
of Modern Physic
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