762 research outputs found
Dissipative dynamics of quantum discord under quantum chaotic environment
We investigate the dissipative dynamics of quantum discord in a decoherence
model with two initially entangled qubits in addition to a quantum kicked top.
The two qubits are uncoupled during the period of our study and one of them
interacts with the quantum kicked top. We find that the long time behavior of
quantum discord could be well described by the fidelity decay of the quantum
kicked top; for short time behavior, however, the phase of the amplitude of the
fidelity decay is necessary to provide more specific information about the
system. We have made comparison between the quantum kicked top and multi-mode
oscillator system in describing environment, and also compared the dynamics of
the entanglement with that of quantum discord.Comment: 5 pages, 3 figures, and Accepted by Europhysics Letter
Long-range quantum discord in critical spin systems
We show that quantum correlations as quantified by quantum discord can
characterize quantum phase transitions by exhibiting nontrivial long-range
decay as a function of distance in spin systems. This is rather different from
the behavior of pairwise entanglement, which is typically short-ranged even in
critical systems. In particular, we find a clear change in the decay rate of
quantum discord as the system crosses a quantum critical point. We illustrate
this phenomenon for first-order, second-order, and infinite-order quantum phase
transitions, indicating that pairwise quantum discord is an appealing quantum
correlation function for condensed matter systems
Constraint handling strategies in Genetic Algorithms application to optimal batch plant design
Optimal batch plant design is a recurrent issue in Process Engineering, which can be formulated as a Mixed Integer Non-Linear Programming(MINLP) optimisation problem involving specific constraints, which can be, typically, the respect of a time horizon for the synthesis of various
products. Genetic Algorithms constitute a common option for the solution of these problems, but their basic operating mode is not always wellsuited to any kind of constraint treatment: if those cannot be integrated in variable encoding or accounted for through adapted genetic operators,
their handling turns to be a thorny issue. The point of this study is thus to test a few constraint handling techniques on a mid-size example in order to determine which one is the best fitted, in the framework of one particular problem formulation. The investigated methods are the elimination of infeasible individuals, the use of a penalty term added in the minimized criterion, the relaxation of the discrete variables upper bounds, dominancebased tournaments and, finally, a multiobjective strategy. The numerical computations, analysed in terms of result quality and of computational time, show the superiority of elimination technique for the former criterion only when the latter one does not become a bottleneck. Besides, when the problem complexity makes the random location of feasible space too difficult, a single tournament technique proves to be the most efficient
one
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
Enhancement of non-equilibrium thermal quantum discord and entanglement of a three-spin XX chain by multi-spin interaction and external magnetic field
We investigate the non-equilibrium thermal quantum discord and entanglement
of a three-spin chain whose two end spins are respectively coupled to two
thermal reservoirs at different temperatures. In the three-spin chain, besides
the XX-type nearest-neighbor two-spin interaction, a multi-spin interaction is
also considered and a homogenous magnetic field is applied to each spin. We
show that the extreme steady-state quantum discord and entanglement of the two
end spins can always be created by holding both a large magnetic field and a
strong multi-spin interaction. The results are explained by the thermal
excitation depression due to switching a large energy gap between the ground
state and the first excited state. The present investigation may provide a
useful approach to control coupling between a quantum system and its
environment.Comment: 16 pages, 10 figure
Frozen and Invariant Quantum Discord under Local Dephasing Noise
In this chapter, we intend to explore and review some remarkable dynamical
properties of quantum discord under various different open quantum system
models. Specifically, our discussion will include several concepts connected to
the phenomena of time invariant and frozen quantum discord. Furthermore, we
will elaborate on the relation of these two phenomena to the non-Markovian
features of the open system dynamics and to the usage of dynamical decoupling
protocols.Comment: 29 pages, 8 figure
Quantum Discord, Decoherence and Quantum Phase Transitions
Quantum discord is a more general measure of quantum correlations than
entanglement and has been proposed as a resource in certain quantum information
processing tasks. The computation of discord is mostly confined to two-qubit
systems for which an analytical calculational scheme is available. The
utilization of quantum correlations in quantum information-based applications
is limited by the problem of decoherence, i.e., the loss of coherence due to
the inevitable interaction of a quantum system with its environment. The
dynamics of quantum correlations due to decoherence may be studied in the Kraus
operator formalism for different types of quantum channels representing
system-environment interactions. In this review, we describe the salient
features of the dynamics of classical and quantum correlations in a two-qubit
system under Markovian (memoryless) time evolution. The two-qubit state
considered is described by the reduced density matrix obtained from the ground
state of a spin model. The models considered include the transverse-field XY
model in one dimension, a special case of which is the transverse-field Ising
model, and the spin chain. The quantum channels studied include the
amplitude damping, bit-flip, bit-phase-flip and phase-flip channels. The Kraus
operator formalism is briefly introduced and the origins of different types of
dynamics discussed. One can identify appropriate quantities associated with the
dynamics of quantum correlations which provide signatures of quantum phase
transitions in the spin models. Experimental observations of the different
types of dynamics are also mentioned.Comment: 20 pages, 6 figures, To appear in Int. J. Mod. Phys. B, special issue
"Classical Vs Quantum correlations in composite systems" edited by L. Amico,
S. Bose, V. Korepin and V. Vedra
Geometric global quantum discord
Geometric quantum discord, proposed by Dakic, Vedral, and Brukner [Phys. Rev.
Lett. 105 (2010) 190502], is an important measure for bipartite correlations.
In this paper, we generalize it to multipartite states, we call the generalized
version geometric global quantum discord (GGQD). We characterize GGQD in
different ways, and provide some special states which allow analytical GGQD.Comment: 8 pages,no figure;added a lower bound for GGQD to version
Multifunctionalized CMCht/PAMAM dendrimer nanoparticles modulate the cellular uptake by astrocytes and oligodendrocytes in primary cultures of glial cells
The efficiency of the treatments involving CNS disorders is commonly diminished by the toxicity, reduced stability and lack of targeting of the administered neuroactive compounds. In this study, we have successfully multifunctionalized CMCht/PAMAM dendrimer nanoparticles by coupling the CD11b antibody and loading MP into the nanoparticles. The modification of the new antibody-conjugated nanoparticles was confirmed by S-TEM observation and 1H NMR and FTIR spectroscopy. Cytotoxicity assays revealed that the conjugates did not affect the viability of both primary cultures of glial and microglial cells. Trace analyses of FITC-labelled nanoparticles revealed that the uptake of antibody-conjugated nanoparticles was conserved in microglial cells but significantly decreased in astrocytes and oligodendrocytes. Thus, this study demonstrates that antibody conjugation contributes to a modulation of the internalization of these nanocarriers by different cell types, which might be of relevance for specific targeting of CNS cell populations.The authors would like to acknowledge the Portuguese Foundation for Science and Technology (Pre-Doctoral fellowship to Susana R. Cerqueira SFRH/BD/48406/2008; Post-Doctoral fellowship to Joaquim M. Oliveira SFRH/BPD/63175/2009; Grant No. PTDC/SAU-BMA/114059/2009; Science 2007 Program - Antonio J. Salgado); the Foundation Calouste de Gulbenkian to funds attributed to Antonio J. Salgado under the scope of the The Gulbenkian Programme to Support Research in the Life Sciences; this work was also partially supported by the European FP7 Project Find and Bind (NMP4-SL-2009-229292)
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