140 research outputs found
Non-Markovian Dynamics of Quantum Discord
We evaluate the quantum discord dynamics of two qubits in independent and
common non-Markovian environments. We compare the dynamics of entanglement with
that of quantum discord. For independent reservoirs the quantum discord
vanishes only at discrete instants whereas the entanglement can disappear
during a finite time interval. For a common reservoir, quantum discord and
entanglement can behave very differently with sudden birth of the former but
not of the latter. Furthermore, in this case the quantum discord dynamics
presents sudden changes in the derivative of its time evolution which is
evidenced by the presence of kinks in its behavior at discrete instants of
time.Comment: 6 pages, 4 figure
Mean excitation numbers due to anti-rotating term (MENDART) in cavity QED under Lindbladian dephasing
We study the photon generation from arbitrary initial state in cavity QED due
to the combined action of the anti-rotating term present in the Rabi
Hamiltonian and Lindblad-type dephasing. We obtain a simple set of differential
equations describing this process and deduce useful formulae for the moments of
the photon number operator, demonstrating analytically that the average photon
number increases linearly with time in the asymptotic limit.Comment: 4 page
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.
Quantum Correlation in One-dimensional Extend Quantum Compass Model
We study the correlations in the one-dimensional extended quantum compass
model in a transverse magnetic field. By exactly solving the Hamiltonian, we
find that the quantum correlation of the ground state of one-dimensional
quantum compass model is vanishing. We show that quantum discord can not only
locate the quantum critical points, but also discern the orders of phase
transitions. Furthermore, entanglement quantified by concurrence is also
compared.Comment: 8 pages, 14 figures, to appear in Eur. Phys. J.
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
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
Exercise training prevents skeletal muscle damage in an experimental sepsis model
OBJECTIVE: Oxidative stress plays an important role in skeletal muscle damage in sepsis. Aerobic exercise can decrease oxidative stress and enhance antioxidant defenses. Therefore, it was hypothesized that aerobic exercise training before a sepsis stimulus could attenuate skeletal muscle damage by modulating oxidative stress. Thus, the aim of this study was to evaluate the effects of aerobic physical preconditioning on the different mechanisms that are involved in sepsis-induced myopathy. METHODS: Male Wistar rats were randomly assigned to either the untrained or trained group. The exercise training protocol consisted of an eight-week treadmill program. After the training protocol, the animals from both groups were randomly assigned to either a sham group or a cecal ligation and perforation surgery group. Thus, the groups were as follows: sham, cecal ligation and perforation, sham trained, and cecal ligation and perforation trained. Five days after surgery, the animals were euthanized and their soleus and plantaris muscles were harvested. Fiber cross-sectional area, creatine kinase, thiobarbituric acid reactive species, carbonyl, catalase and superoxide dismutase activities were measured. RESULTS: The fiber cross-sectional area was smaller, and the creatine kinase, thiobarbituric acid reactive species and carbonyl levels were higher in both muscles in the cecal ligation and perforation group than in the sham and cecal ligation and perforation trained groups. The muscle superoxide dismutase activity was higher in the cecal ligation and perforation trained group than in the sham and cecal ligation and perforation groups. The muscle catalase activity was lower in the cecal ligation and perforation group than in the sham group. CONCLUSION: In summary, aerobic physical preconditioning prevents atrophy, lipid peroxidation and protein oxidation and improves superoxide dismutase activity in the skeletal muscles of septic rats
Quantum discord evolution of three-qubit states under noisy channels
We investigated the dissipative dynamics of quantum discord for correlated
qubits under Markovian environments.
The basic idea in the present scheme is that quantum discord is more general,
and possibly more robust and fundamental, than entanglement. We provide three
initially correlated qubits in pure Greenberger-Horne-Zeilinger (GHZ) or W
state and analyse the time evolution of the quantum discord under various
dissipative channels such as:
Pauli channels , , and , as well as
depolarising channels. Surprisingly, we find that under the action of Pauli
channel , the quantum discord of GHZ state is not affected by
decoherence. For the remaining dissipative channels, the W state is more robust
than the GHZ state against decoherence. Moreover, we compare the dynamics of
entanglement with that of the quantum discord under the conditions in which
disentanglement occurs and show that quantum discord is more robust than
entanglement except for phase flip coupling of the three qubits system to the
environment.Comment: 17 pages, 4 figures, accepted for publication in EPJ
Could a remarkable decrease in leptin and insulin levels from colostrum to mature milk contribute to early growth catch-up of SGA infants?
Background: Breast milk is known to contain many bioactive hormones and peptides, which can influence infant growth and development. In this context, the purpose of this study was to evaluate the influence of different clinical pregnancy conditions on hormone concentrations in colostrum and mature breast milk. Methods: An observational study was performed with mother-newborn pairs divided into five groups according to maternal clinical background: diabetes (12), hypertension (5), smoking (19), intrauterine growth restriction of unknown causes with small-for-gestational-age newborns at delivery (12), and controls (21). Socioeconomic data, anthropometric measurements and breast milk samples were collected between the first 24 and 48 h and 30 days postpartum. Leptin, adiponectin, and insulin levels in breast milk were measured by immunoassays. Results: A significant decrease in leptin (p = 0.050) and insulin (p = 0.012) levels from colostrum to mature breast milk in mothers of small-for-gestational-age infants was observed. Maternal body mass index was correlated with both leptin and insulin, but not with adiponectin. Insulin levels were negatively correlated to infant weight gain from birth to one month (p = 0.050). In addition, catch-up growth was verified for small-for-gestational-age infants throughout the first month of life. Conclusions: This study suggests that a remarkable decrease in leptin and insulin levels in mature milk of mothers of small-for-gestational-age newborns may be involved in the rapid weight gain of these newborns. The physiological and external mechanisms by which these significant decreases and rapid weight gains occur in this group remain to be elucidated
- âŠ