Sudden change in the behavior of quantum discord for bipartite Gisin states

2018 ◽  
Vol 15 (03) ◽  
pp. 1850038 ◽  
Author(s):  
Fatima-Zahra Siyouri ◽  
Mustapha Ziane ◽  
Morad El Baz ◽  
Yassine Hassouni
Keyword(s):  
Quantum System ◽  
Quantum Correlation ◽  
Coherent States ◽  
Quantum Discord ◽  
Sudden Change ◽  
Classical Correlation ◽  
Mixing Parameter

In this paper, we investigate the behavior of quantum correlation for Gisin states based on the bipartite superposed coherent states (SCS). Moreover, we analyze the basis for minimizing the quantum discord (or equivalently basis maximizing the classical correlation) as function of the mixing parameter and the coherent amplitude. We found that for our quantum system, the quantum discord behavior is not smooth and could experience a sudden change (S.C).

scholarly journals SUDDEN CHANGE OF QUANTUM DISCORD UNDER SINGLE QUBIT NOISE

2013 ◽  
Vol 11 (05) ◽  
pp. 1350048 ◽  
Author(s):  
LI-XING JIA ◽  
BO LI ◽  
R.-H. YUE ◽  
HENG FAN
Keyword(s):  
Quantum System ◽  
Quantum Correlation ◽  
Quantum Discord ◽  
Sudden Change ◽  
Entangled State ◽  
Noisy Environment ◽  
Noisy Environments ◽  
Single Qubit ◽  
Sudden Transition

We show that the sudden change of quantum correlation can occur even when only one part of the composite entangled state is exposed to a noisy environment. Our results are illustrated through the action of different noisy environments individually on a single qubit of quantum system. Composite noise on the whole of the quantum system is thus not the necessarily condition for the occurrence of sudden transition for quantum correlation.

Quantum discord of a three-qubit W-class state in noisy environments

2012 ◽  
Vol 12 (7&8) ◽  
pp. 677-692
Author(s):  
Hui Guo ◽  
Jin-Ming Liu ◽  
Cheng-Jie Zhang ◽  
C. H. Oh
Keyword(s):  
Numerical Analysis ◽  
Sudden Death ◽  
Quantum Correlation ◽  
Quantum Discord ◽  
Sudden Change ◽  
Noisy Environments ◽  
Classical Correlation ◽  
Entanglement Of Formation ◽  
Sudden Transition ◽  
Bit Flip

We study the dynamics of the pairwise quantum discord (QD), classical correlation (CC), and entanglement of formation (EOF) for the three-qubit W-class state |W>_{123}=\frac 12(|100>_{123}+|010>_{123}+\sqrt{2}|001>_{123}) under the influence of various Markovian noises by analytically solving the master equation in the Lindblad form. Through numerical analysis, we find that EOF decreases asymptotically to zero with time for the dephasing noise, but it undergoes sudden death for the bit-flip noise, the isotropic noise, as well as the dissipative and noisy environments. Moreover, QD decays to zero in an asymptotical way for all the noises we investigated. Thus, when the W-class state |W>_{123} is subject to the above Markovian noises, QD is more robust than EOF against decoherence excluding the phase-flip noise, implying that QD is more useful than entanglement to characterize the quantum correlation. We also find a remarkable character for the CC in the presence of the phase-flip noise, i.e., CC displays the behavior of sudden transition and then keeps constant permanently, but the corresponding QD just exhibits a very small sudden change. Furthermore, we verify the monogamic relation between the pairwise QD and EOF of the W-class state.

Measurement of quantum correlation by Frobenius norm in non-Markovian system

2018 ◽  
Vol 16 (03) ◽  
pp. 1850022 ◽  
Author(s):  
Juju Hu ◽  
Shuqin Liu ◽  
Yinghua Ji
Keyword(s):  
Density Matrix ◽  
Quantum System ◽  
Quantum Correlation ◽  
Quantum Discord ◽  
Frobenius Norm ◽  
Easy Method ◽  
Test Matrix ◽  
Research Results ◽  
Bipartite State ◽  
Markovian System

In order to measure the quantum correlation of a bipartite state quickly, an easy method is to construct a test matrix through the commutations among the blocks of its density matrix. Then, the Frobenius norm of the test matrix can be used to measure the quantum correlation. In this paper, we apply the measurement by Frobenius norm ([Formula: see text] to the dynamics evolution of the non-Markovian quantum system and compare it with the typical quantum discord ([Formula: see text] proposed by Ollivier and Zurek. The research results show that [Formula: see text] can indeed measure the quantum correlation of a bipartite state as same as [Formula: see text]. Further studies find that there are still differences between the two measurements: in some regions, when [Formula: see text] is zero, [Formula: see text] is not zero. It indicates that [Formula: see text] is more detailed than [Formula: see text] to measure quantum correlation of a bipartite state.

Improvement of quantum correlations by repetitive quantum error correction

2019 ◽  
Vol 17 (05) ◽  
pp. 1950044
Author(s):  
A. El Allati ◽  
H. Amellal ◽  
A. Meslouhi
Keyword(s):  
Error Correction ◽  
Quantum Correlation ◽  
Coherent States ◽  
Quantum Discord ◽  
Error Correcting Code ◽  
Quantum Correlations ◽  
Quantum Error Correction ◽  
Optical Field ◽  
Quantum Error ◽  
Entangled Coherent States

A quantum error-correcting code is established in entangled coherent states (CSs) with Markovian and non-Markovian environments. However, the dynamic behavior of these optical states is discussed in terms of quantum correlation measurements, entanglement and discord. By using the correcting codes, these correlations can be as robust as possible against environmental effects. As the number of redundant CSs increases due to the repetitive error correction, the probabilities of success also increase significantly. Based on different optical field parameters, the discord can withstand more than an entanglement. Furthermore, the behavior of quantum discord under decoherence may exhibit sudden death and sudden birth phenomena as functions of dimensionless parameters.

Non-Markovian dynamics of correlations: The composite effect of two channels and robust quantum correlation preserving by detuning

2014 ◽  
Vol 29 (02) ◽  
pp. 1450249
Author(s):  
Y. H. Ji ◽  
X. D. Wan
Keyword(s):  
Quantum Information ◽  
Quantum Correlation ◽  
Quantum Discord ◽  
Quantum Information Processing ◽  
Center Frequency ◽  
Cavity Model ◽  
Classical Correlation ◽  
Composite Effect ◽  
Markovian Dynamics ◽  
Dynamics Of Correlations

We investigate the influence of the composite effect and information backflow effect in non-Markovian channel on the dynamics of quantum correlation including quantum entanglement and quantum discord. It is found that, the composite effect of independent channels is not only harmful to the maintenance of quantum correlation but also unfavorable for the maintenance of classic correlation. In a non-Markovian channel, by regulating the discord between qubit and the center frequency of cavity model, the time of quantum correlation and classical correlation of the system can be effectively prolonged. Thus, the quantum information processing can be achieved more easily under larger detuning.

scholarly journals The witness of sudden change of geometric quantum correlation

2014 ◽  
Vol 14 (5&6) ◽  
pp. 454-466
Author(s):  
Chang-shui Yu ◽  
Bo Li ◽  
Heng Fan
Keyword(s):  
Critical Points ◽  
Quantum Correlation ◽  
Quantum Discord ◽  
Graphical Representation ◽  
Sudden Change ◽  
Necessary Condition ◽  
Correlation Measure ◽  
Geometric Quantum Discord ◽  
Definition Of ◽  
Sufficient And Necessary Condition

In this paper, we give a sufficient and necessary condition (witness) for the sudden change of geometric quantum discord by considering mathematical definition of the discontinuity of a function. Based on the witness, we can find out various sudden changes of quantum correlation by considering both the Markovian and the non-Markovian cases. In particular, we can accurately find out critical points of the sudden changes even though they are not quite obvious in the graphical representation. In addition, one can also find that sudden change of quantum correlation, like the frozen quantum correlation, strongly depends on the choice of the quantum correlation measure.

scholarly journals Non-monogamy of quantum discord and upper bounds for quantum correlation

2013 ◽  
Vol 13 (5&6) ◽  
pp. 469-478
Author(s):  
Xi-Jun Ren ◽  
Heng Fan
Keyword(s):  
Mutual Information ◽  
Quantum Correlation ◽  
Quantum Discord ◽  
Quantum Correlations ◽  
Upper Bounds ◽  
Physical Analysis ◽  
Classical Correlation ◽  
Entanglement Of Formation ◽  
Quantum Mutual Information ◽  
Bipartite States

We consider a monogamy inequality of quantum discord in a pure tripartite state and show that it is equivalent to an inequality between quantum mutual information and entanglement of formation of two parties. Since this inequality does not hold for arbitrary bipartite states, quantum discord can generally be both monogamous and polygamous. We also carry out numerical calculations for some special states. The upper bounds of quantum discord and classical correlation are also discussed and we give physical analysis on the invalidness of a previous conjectured upper bound of quantum correlation. Our results provide new insights for further understanding of distributions of quantum correlations.

scholarly journals QUANTUM DISCORD FOR MULTIPARTITE COHERENT STATES INTERPOLATING BETWEEN WERNER AND GREENBERGER–HORNE–ZEILINGER STATES

2012 ◽  
Vol 10 (05) ◽  
pp. 1250060 ◽  
Author(s):  
M. DAOUD ◽  
R. AHL LAAMARA
Keyword(s):  
Quantum System ◽  
Ground State ◽  
Coherent States ◽  
Quantum Discord ◽  
Temporal Evolution ◽  
Conditional Entropy ◽  
Quantum Correlations ◽  
Ghz States ◽  
Werner States ◽  
Explicit Expressions

The quantum discord is used as measure of quantum correlations for two families of multipartite coherent states. The first family interpolates between generalized GHZ states and generalized Werner states. The second one is an interpolation between generalized GHZ and the ground state of the multipartite quantum system. Two inequivalent ways to split the system in a pair of qubits are introduced. The explicit expressions of quantum quantum discord in multipartite coherent states are derived. Its evaluation uses the Koashi–Winter relation in optimizing the conditional entropy. The temporal evolution of quantum correlations (quantum discord and entanglement) is also discussed.

The impact of resource on remote quantum correlation Preparation

2015 ◽  
Vol 15 (13&14) ◽  
pp. 1223-1232
Author(s):  
Chengjun Wu ◽  
Bin Luo ◽  
Hong Guo
Keyword(s):  
Quantum Entanglement ◽  
Quantum Correlation ◽  
Quantum Discord ◽  
Entangled States ◽  
Shared Resources ◽  
Classical Communication ◽  
Bell Measurement ◽  
Measurement Results ◽  
The Impact

When Alice and Bob share two pairs of quantum correlated states, Alice can remotely prepare quantum entanglement and quantum discord in Bob’s side by measuring the parts in her side and telling Bob the measurement results by classical communication. For remote entanglement preparation, entanglement is necessary . We find that for some shared resources having the same amount of entanglement, when Bell measurement is used, the entanglement remotely prepared can be different, and more discord in the resources actually decreases the entanglement prepared. We also find that for some resources with more entanglement, the entanglement remotely prepared may be less. Therefore, we conclude that entanglement is a necessary resource but may not be the only resource responsible for the entanglement remotely prepared, and discord does not likely to assist this process. Also, for the preparation of discord, we find that some states with no entanglement could outperform entangled states.

scholarly journals Quantum Filtering Equations for a System Driven by Nonclassical Fields

2018 ◽  
Vol 25 (02) ◽  
pp. 1850007 ◽  
Author(s):  
Anita Da̧browska
Keyword(s):  
Quantum System ◽  
Coherent States ◽  
Single Photon ◽  
Photon Counting ◽  
Stochastic Evolution ◽  
Input Output ◽  
Nonclassical States ◽  
Cascade System ◽  
Unitary Evolution ◽  
Photon States

Using Gardiner and Collet’s input-output model and the concept of cascade system, we determine the filtering equation for a quantum system driven by light in some specific nonclassical states. The quantum system and electromagnetic field are described by making use of quantum stochastic unitary evolution. We consider two examples of the nonclassical states of field: a combination of vacuum and single photon states and a mixture of two coherent states. The stochastic evolution conditioned on the results of the photon counting and quadrature measurements is described.

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