140 research outputs found
Generation of decoherence-free displaced squeezed states of radiation fields and a squeezed reservoir for atoms in cavity QED
We present a way to engineer an effective anti-Jaynes-Cumming and a
Jaynes-Cumming interaction between an atomic system and a single cavity mode
and show how to employ it in reservoir engineering processes. To construct the
effective Hamiltonian, we analyse considered the interaction of an atomic
system in a \{Lambda} configuration, driven by classical fields, with a single
cavity mode. With this interaction, we firstly show how to generate a
decoherence-free displaced squeezed state for the cavity field. In our scheme,
an atomic beam works as a reservoir for the radiation field trapped inside the
cavity, as employed recently by S. Pielawa et al. [Phys. Rev. Lett. 98, 240401
(2007)] to generate an Einstein-Podolsky-Rosen entangled radiation state in
high-Q resonators. In our scheme, all the atoms have to be prepared in the
ground state and, as in the cited article, neither atomic detection nor precise
interaction times between the atoms and the cavity mode are required. From this
same interaction, we can also generate an ideal squeezed reservoir for atomic
systems. For this purpose we have to assume, besides the engineered atom-field
interaction, a strong decay of the cavity field (i.e., the cavity decay must be
much stronger than the effective atom-field coupling). With this scheme, some
interesting effects in the dynamics of an atom in a squeezed reservoir could be
tested
Decoherence Dynamics of Measurement-Induced Nonlocality and comparison with Geometric Discord for two qubit systems
We check the decoherence dynamics of Measurement-induced Nonlocality(in
short, MIN) and compare it with geometric discord for two qubit systems. There
are quantum states, on which the action of dephasing channel cannot destroy MIN
in finite or infinite time. We check the additive dynamics of MIN on a qubit
state under two independent noise. Geometric discord also follows such additive
dynamics like quantum discord. We have further compared non-Markovian evolution
of MIN and geometric discord under dephasing and amplitude damping noise for
pure state and it shows distinct differences between their dynamics.Comment: 11 pages, 10 figures, Revte
Transverse Ising Model: Markovian evolution of classical and quantum correlations under decoherence
The transverse Ising Model (TIM) in one dimension is the simplest model which
exhibits a quantum phase transition (QPT). Quantities related to quantum
information theoretic measures like entanglement, quantum discord (QD) and
fidelity are known to provide signatures of QPTs. The issue is less well
explored when the quantum system is subjected to decoherence due to its
interaction, represented by a quantum channel, with an environment. In this
paper we study the dynamics of the mutual information , the
classical correlations and the quantum correlations
, as measured by the QD, in a two-qubit state the density matrix
of which is the reduced density matrix obtained from the ground state of the
TIM in 1d. The time evolution brought about by system-environment interactions
is assumed to be Markovian in nature and the quantum channels considered are
amplitude damping, bit-flip, phase-flip and bit-phase-flip. Each quantum
channel is shown to be distinguished by a specific type of dynamics. In the
case of the phase-flip channel, there is a finite time interval in which the
quantum correlations are larger in magnitude than the classical correlations.
For this channel as well as the bit-phase-flip channel, appropriate quantities
associated with the dynamics of the correlations can be derived which signal
the occurrence of a QPT.Comment: 8 pages, 7 figures, revtex4-1, version accepted for publication in
Eur. Phys. J.
Detection of salmonella heidelberg resistant to colistin in the intestinal content of pigs at slaughter.
Abstract : Salmonella Heidelberg has increasingly been reported as cause of human salmonellosis worldwide. In Brazil, S. Heidelberg has been reported in poultry but it is infrequently isolated from pigs. Here, we describe the isolation of S. Heidelberg resistant to colistin from slaughter pigs. Five pigs and their carcasses belonging to a same slaughter batch in ten consecutive days were sampled for fragment of intestine in the ileocecal region and sponges rubbed on the carcass surface (400 cm2 ) before chilling. Salmonella detection was performed according to the ISO 6579:2002. Intestinal content was also subjected to Salmonella enumeration by a miniaturized Most Probable Number (MPN) protocol. Salmonella isolates were characterized by antimicrobial resistance by the disk diffusion test, the minimum inhibitory concentration to colistin determination and to gene mcr-1 investigation by PCR. Salmonella was isolated from the intestinal content of 64% (32/50) of the pigs, in amounts that varied from 2.7 to >1,400 MPN/g. Salmonella Heidelberg was the most frequent serovar identified in the intestinal content samples (20/50; 40%), and this serovar was present in eight of the ten pig batches sampled. At the prechill, Salmonella was isolated from 8% of carcasses, and S. Heidelberg was not detected. Salmonella Heidelberg strains were resistant against ampicillin (n=9), tetracycline (n=8), sulfonamide (n=8) and gentamicin (n=5). Nine multi-drug resistant strains were detected; among them four strains were positive for the gene mcr-1. In these strains the MIC value was 8 µg.mL-1 , while in the strains without the mcr-1 gene it ranged from 2 µg.mL-1 to 4 µg.mL-1 . Therefore, humans in contact with carrier pigs or their environment may be exposed to S. Heidelberg, including strains harboring the gene mcr-1.SafePork 2017
Quantum correlations in a few-atom spin-1 Bose-Hubbard model
We study the thermal quantum correlations and entanglement in spin-1 Bose-Hubbard model with two and three particles. While we use negativity to calculate entanglement, more general non-classical correlations are quantified using a new measure based on a necessary and sufficient condition for zero-discord state. We demonstrate that the energy level crossings in the ground state of the system are signalled by both the behavior of thermal quantum correlations and entanglement
Quantum Discord and entropic measures of quantum correlations: Optimization and behavior in finite spin chains
We discuss a generalization of the conditional entropy and one-way
information deficit in quantum systems, based on general entropic forms. The
formalism allows to consider simple entropic forms for which a closed
evaluation of the associated optimization problem in qudit-qubit systems is
shown to become feasible, allowing to approximate that of the quantum discord.
As application, we examine quantum correlations of spin pairs in the exact
ground state of finite spin chains in a magnetic field through the quantum
discord and information deficit. While these quantities show a similar
behavior, their optimizing measurements exhibit significant differences, which
can be understood and predicted through the previous approximations. The
remarkable behavior of these quantities in the vicinity of transverse and
non-transverse factorizing fields is also discussed.Comment: 10 pages, 3 figure
Algebraic characterization of X-states in quantum information
A class of two-qubit states called X-states are increasingly being used to
discuss entanglement and other quantum correlations in the field of quantum
information. Maximally entangled Bell states and "Werner" states are subsets of
them. Apart from being so named because their density matrix looks like the
letter X, there is not as yet any characterization of them. The su(2) X su(2) X
u(1) subalgebra of the full su(4) algebra of two qubits is pointed out as the
underlying invariance of this class of states. X-states are a seven-parameter
family associated with this subalgebra of seven operators. This recognition
provides a route to preparing such states and also a convenient algebraic
procedure for analytically calculating their properties. At the same time, it
points to other groups of seven-parameter states that, while not at first sight
appearing similar, are also invariant under the same subalgebra. And it opens
the way to analyzing invariant states of other subalgebras in bipartite
systems.Comment: 4 pages, 1 figur
Markovian evolution of classical and quantum correlations in transverse-field XY model
The transverse-field XY model in one dimension is a well-known spin model for
which the ground state properties and excitation spectrum are known exactly.
The model has an interesting phase diagram describing quantum phase transitions
(QPTs) belonging to two different universality classes. These are the
transverse-field Ising model and the XX model universality classes with both
the models being special cases of the transverse-field XY model. In recent
years, quantities related to quantum information theoretic measures like
entanglement, quantum discord (QD) and fidelity have been shown to provide
signatures of QPTs. Another interesting issue is that of decoherence to which a
quantum system is subjected due to its interaction, represented by a quantum
channel, with an environment. In this paper, we determine the dynamics of
different types of correlations present in a quantum system, namely, the mutual
information, the classical correlations and the quantum correlations, as
measured by the quantum discord, in a two-qubit state. The density matrix of
this state is given by the nearest-neighbour reduced density matrix obtained
from the ground state of the transverse-field XY model in 1d. We assume
Markovian dynamics for the time-evolution due to system-environment
interactions. The quantum channels considered include the bit-flip,
bit-phase-flip and phase-flip channels. Two different types of dynamics are
identified for the channels in one of which the quantum correlations are
greater in magnitude than the classical correlations in a finite time interval.
The origins of the different types of dynamics are further explained. For the
different channels, appropriate quantities associated with the dynamics of the
correlations are identified which provide signatures of QPTs. We also report
results for further-neighbour two-qubit states and finite temperatures.Comment: 10 pages, 11 figures, revtex4-1. arXiv admin note: text overlap with
arXiv:1205.130
Geometric measure of quantum discord and the geometry of a class of two-qubit states
We investigate the geometric picture of the level surfaces of quantum
entanglement and geometric measure of quantum discord (GMQD) of a class of
X-states, respectively. This pictorial approach provides us a direct
understanding of the structure of entanglement and GMQD. The dynamic evolution
of GMQD under two typical kinds of quantum decoherence channels is also
investigated. It is shown that there exists a class of initial states for which
the GMQD is not destroyed by decoherence in a finite time interval.
Furthermore, we establish a factorization law between the initial and final
GMQD, which allows us to infer the evolution of entanglement under the
influences of the environment.Comment: 10 pages, 4 figures, comments are welcom
Conditions for the freezing phenomena of geometric measure of quantum discord for arbitrary two-qubit X states under non-dissipative dephasing noises
We study the dynamics of geometric measure of quantum discord (GMQD) under
the influences of two local phase damping noises. Consider the two qubits
initially in arbitrary X-states, we find the necessary and sufficient
conditions for which GMQD is unaffected for a finite period. It is further
shown that such results also hold for the non-Markovian dephasing process.Comment: 4 pages, 2 figure
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