212 research outputs found
Factorization and Criticality in the Anisotropic XY Chain via Correlations
In this review, we discuss the zero and finite temperature behavior of
various bipartite quantum and total correlation measures, the skew
information-based quantum coherence, and the local quantum uncertainty in the
thermal ground state of the one-dimensional anisotropic XY model in transverse
magnetic field. We compare the ability of considered measures to correctly
detect or estimate the quantum critical point and the non-trivial factorization
point possessed by the spin chain.Comment: 29 pages, 8 figures. A review paper accepted for publication in the
special issue Entanglement Entropy in the journal Entrop
Drought Analysis for 2007-2008 Agricultural Year of Turkey
Drought is among the most significant natural disasters and has severe economical, social and environmental impacts. It is somehow different from the other natural disasters since it is hard to determine exact start and end dates of drought. Drought gradually increases its severity and may keep its effects for years after the end of drought. Effects of drought is initially observed in agriculture and diffused gradually into waterrelated sectors. The recent global drought and utilization of agricultural crops for bio-fuel production has created significant problems in food supply. For instance, as a result of the drought experienced in the year of 2007, wheat production was not sufficient. Beside this, consumption increased for bio-fuel production and wheat prices in international markets increased by 3 folds. These problems observed in basic agricultural crops like maize and rice has brought forward the significance of continuous drought monitoring and analysis. In this study, the drought experienced in 2007-2008 Agricultural Year of Turkey was analyzed and contributions were tried to be made for future production activities. The drought was evaluated by using Standardized Precipitation Index (SPI), Percent of Normal Index (PNI) and the analyses of precipitation and temperature analysis
Protecting the operation from general and residual errors by continuous dynamical decoupling
We study the occurrence of errors in a continuously decoupled two-qubit state
during a quantum operation under decoherence. We consider a
realization of this quantum gate based on the Heisenberg exchange interaction,
which alone suffices for achieving universal quantum computation. Furthermore,
we introduce a continuous-dynamical-decoupling scheme that commutes with the
Heisenberg Hamiltonian to protect it from the amplitude damping and dephasing
errors caused by the system-environment interaction. We consider two
error-protection settings. One protects the qubits from both amplitude damping
and dephasing errors. The other features the amplitude damping as a residual
error and protects the qubits from dephasing errors only. In both settings, we
investigate the interaction of qubits with common and independent environments
separately. We study how errors affect the entanglement and fidelity for
different environmental spectral densities.Comment: Extended version of arXiv:1005.1666. To appear in PR
Quantum Correlations and Coherence in Spin-1 Heisenberg Chains
We explore quantum and classical correlations along with coherence in the
ground states of spin-1 Heisenberg chains, namely the one-dimensional XXZ model
and the one-dimensional bilinear biquadratic model, with the techniques of
density matrix renormalization group theory. Exploiting the tools of quantum
information theory, that is, by studying quantum discord, quantum mutual
information and three recently introduced coherence measures in the reduced
density matrix of two nearest neighbor spins in the bulk, we investigate the
quantum phase transitions and special symmetry points in these models. We point
out the relative strengths and weaknesses of correlation and coherence measures
as figures of merit to witness the quantum phase transitions and symmetry
points in the considered spin-1 Heisenberg chains. In particular, we
demonstrate that as none of the studied measures can detect the infinite order
Kosterlitz-Thouless transition in the XXZ model, they appear to be able to
signal the existence of the same type of transition in the biliear biquadratic
model. However, we argue that what is actually detected by the measures here is
the SU(3) symmetry point of the model rather than the infinite order quantum
phase transition. Moreover, we show in the XXZ model that examining even single
site coherence can be sufficient to spotlight the second-order phase transition
and the SU(2) symmetry point.Comment: 8 pages. 5 figure
Quantum coherence and uncertainty in the anisotropic XY chain
We explore the local quantum coherence and the local quantum uncertainty,
based on Wigner-Yanase skew information, in the ground state of the anisotropic
spin-1/2 XY chain in transverse magnetic field. We show that the skew
information, as a figure of merit, supplies the necessary information to reveal
the occurrence of the second order phase transition and the completely
factorized ground state in the XY model. Additionally, in the same context, we
also discuss the usefulness of a simple experimentally friendly lower bound of
local quantum coherence. Furthermore, we demonstrate how the connection between
the appearance of non-analyticities in the local quantum uncertainty of the
ground state and the quantum phase transitions does not hold in general, by
providing explicit examples of the situation. Lastly, we discuss the ability of
the local quantum coherence to accurately estimate the critical point of the
phase transition, and investigate the robustness of the factorization
phenomenon at low temperatures.Comment: 7 pages, 6 figures. Title changed. Close to published versio
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