380 research outputs found
Implementing Quantum Gates using the Ferromagnetic Spin-J XXZ Chain with Kink Boundary Conditions
We demonstrate an implementation scheme for constructing quantum gates using
unitary evolutions of the one-dimensional spin-J ferromagnetic XXZ chain. We
present numerical results based on simulations of the chain using the
time-dependent DMRG method and techniques from optimal control theory. Using
only a few control parameters, we find that it is possible to implement one-
and two-qubit gates on a system of spin-3/2 XXZ chains, such as Not, Hadamard,
Pi-8, Phase, and C-Not, with fidelity levels exceeding 99%.Comment: Updated Acknowledgement
The number of irreducible polynomials of degree n over Fq with given trace and constant terms
AbstractWe study the number Nγ(n,c,q) of irreducible polynomials of degree n over Fq where the trace γ and the constant term c are given. Under certain conditions on n and q, we obtain bounds on the maximum of Nγ(n,c,q) varying c and γ. We show with concrete examples how our results improve the previously known bounds. In addition, we improve upper and lower bounds of any Nγ(n,c,q) when n=a(q−1) for a nonzero constant term c and a nonzero trace γ. As a byproduct, we give a simple and explicit formula for the number N(n,c,q) of irreducible polynomials over Fq of degree n=q−1 with a prescribed primitive constant term c
Decay of Superconducting and Magnetic Correlations in One- and Two-Dimensional Hubbard Models
In a general class of one and two dimensional Hubbard models, we prove upper
bounds for the two-point correlation functions at finite temperatures for
electrons, for electron pairs, and for spins. The upper bounds decay
exponentially in one dimension, and with power laws in two dimensions. The
bounds rule out the possibility of the corresponding condensation of
superconducting electron pairs, and of the corresponding magnetic ordering. Our
method is general enough to cover other models such as the t-J model.Comment: LaTeX, 8 pages, no figures. A reference appeared after the
publication is adde
Numerical evidence of chiral magnetic effect in lattice gauge theory
The chiral magnetic effect is the generation of electric current of quarks
along external magnetic field in the background of topologically nontrivial
gluon fields. There is a recent evidence that this effect is observed by the
STAR Collaboration in heavy ion collisions at RHIC. In our paper we study
qualitative signatures of the chiral magnetic effect using quenched lattice
simulations. We find indications that the electric current is indeed enhanced
in the direction of the magnetic field both in equilibrium configurations of
the quantum gluon fields and in a smooth gluon background with nonzero
topological charge. In the confinement phase the magnetic field enhances the
local fluctuations of both the electric charge and chiral charge densities. In
the deconfinement phase the effects of the magnetic field become smaller,
possibly due to thermal screening. Using a simple model of a fireball we obtain
a good agreement between our data and experimental results of the STAR
Collaboration.Comment: 14 pages, 14 figures, uses RevTeX 4.0; revision: references and
comments added, figures corrected, published versio
From Ground States to Local Hamiltonians
Traditional quantum physics solves ground states for a given Hamiltonian,
while quantum information science asks for the existence and construction of
certain Hamiltonians for given ground states. In practical situations, one
would be mainly interested in local Hamiltonians with certain interaction
patterns, such as nearest neighbour interactions on some type of lattices. A
necessary condition for a space to be the ground-state space of some local
Hamiltonian with a given interaction pattern, is that the maximally mixed state
supported on is uniquely determined by its reduced density matrices
associated with the given pattern, based on the principle of maximum entropy.
However, it is unclear whether this condition is in general also sufficient. We
examine the situations for the existence of such a local Hamiltonian to have
satisfying the necessary condition mentioned above as its ground-state
space, by linking to faces of the convex body of the local reduced states. We
further discuss some methods for constructing the corresponding local
Hamiltonians with given interaction patterns, mainly from physical points of
view, including constructions related to perturbation methods, local
frustration-free Hamiltonians, as well as thermodynamical ensembles.Comment: 11 pages, 2 figures, to be published in PR
Mutual Exclusion Statistics in Exactly Solvable Models in One and Higher Dimensions at Low Temperatures
We study statistical characterization of the many-body states in exactly
solvable models with internal degrees of freedom. The models under
consideration include the isotropic and anisotropic Heisenberg spin chain, the
Hubbard chain, and a model in higher dimensions which exhibits the Mott
metal-insulator transition. It is shown that the ground state of these systems
is all described by that of a generalized ideal gas of particles (called
exclusons) which have mutual exclusion statistics, either between different
rapidities or between different species. For the Bethe ansatz solvable models,
the low temperature properties are well described by the excluson description
if the degeneracies due to string solutions with complex rapidities are taken
into account correctly. {For} the Hubbard chain with strong but finite
coupling, charge-spin separation is shown for thermodynamics at low
temperatures. Moreover, we present an exactly solvable model in arbitrary
dimensions which, in addition to giving a perspective view of spin-charge
separation, constitutes an explicit example of mutual exclusion statistics in
more than two dimensions
Heavy quark potential in lattice QCD at finite temperature
Results of the study of lattice QCD with two flavors of nonperturbatively
improved Wilson fermions at finite temperature are presented. The transition
temperature for m_{\pi}/m_{\rho} \sim 0.8 and lattice spacing a \sim 0.12 fm is
determined. A two-exponent ansatz is successfully applied to describe the heavy
quark potential in the confinement phase.Comment: 3 pages, 1 figure, talk given at the 5th International Conference on
Quark Confinement and the Hadron Spectrum, Gargnano, Italy, 10-14 Sep 200
Cluster Property and Robustness of Ground States of Interacting Many Bosons
We study spatial correlation functions of local operators of interacting many
bosons confined in a box of a large, but volume V, for various `ground states'
whose energy densities are almost degenerate. The ground states include the
coherent state of interacting bosons (CSIB), the number state of interacting
bosons (NSIB), and the number-phase squeezed state of interacting bosons, which
interpolates between the CSIB and NSIB. It was shown previously that only the
CSIB is robust (i.e., does not decohere for a macroscopically long time)
against the leakage of bosons into an environment. We show that for the CSIB
the spatial correlation of any local operators A(r) and B(r') (which are
localized around r and r', respectively) vanishes as |r - r' | \sim V^{1/3} \to
\infty, i.e., the CSIB has the `cluster property.' In contrast, the other
ground states do not possess the cluster property. Therefore, we have
successfully shown that the robust state has the cluster property. This ensures
the consistency of the field theory of bosons with macroscopic theories.Comment: We have replaced the manuscript in order to update the reference list
and to fix typos. (5 pages, no figures) In the final manuscript, a few
sentences have added for more detailed explanation. Journal PDF at
http://jpsj.jps.or.jp/journal/JPSJ-71-1.htm
Cost-effective therapy remission assessment in lymphoma patients using 2-[fluorine-18]fluoro-2-deoxy-D-glucose-positron emission tomography/computed tomography: is an end of treatment exam necessary in all patients?
Background: The aim of this study was to evaluate the necessity of 2-[fluorine-18]fluoro-2-deoxy-D-glucose-positron emission tomography/computed tomography (FDG-PET/CT) after end of treatment in lymphoma patients who had an interim FDG-PET/CT. Patients and methods: In 38 patients with Hodgkin's disease (HD) and 30 patients with non-Hodgkin's lymphoma (NHL) interim PET/CT (intPET) after two to four cycles of chemotherapy and PET/CT after completion of first-line treatment (endPET) were carried out. Cost reduction was retrospectively calculated for the potentially superfluous endPET examinations. Results: In 31 (82%) HD patients, intPET demonstrated complete remission (CR) which was still present on endPET. The remaining seven HD patients (18%) had partial remission (PR) on intPET. For NHL, 22 (73%) patients had CR on intPET analysis which was still present on endPET. In the remaining eight NHL patients, intPET revealed PR in seven and stable disease in one patient. None of all intPET complete responders progressed until the end of therapy. Thus, of the 196 PET/CT's carried out in our study population, 53 endPET's (27.0%) were carried out in interim complete responders. Conclusion: End-treatment PET/CT is unnecessary if intPET shows CR and the clinical course is uncomplicated. An imaging cost reduction of 27% in our study population could have been achieved by omitting end of treatment FDG-PET/CT in interim complete responder
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