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ABSTRACT: In this work, we study the effects of different forms of correlations of environments on the dynamics of open
systems’ entanglement and discord. We consider two two-level atoms A and B interacting, respectively with
two spatially separated modes a and b, each of which is in turn surrounded by a dissipative reservoir. The
two modes may initially be in an entangled or classically correlated or product state with their marginal state
being the same in all the cases. We compare the power of different environmental correlation forms in the revival
of the atoms’ entanglement and discord in the strong atom–mode coupling regime. We also show how the dynamical
behavior of the atoms’ entanglement and discord nontrivially change by the presence of initial environmental
correlation in the weak atom–mode coupling regime. Finally, we reveal that initial entanglement between the
modes can induce correlations between initially uncorrelated atoms.
Journal of the Optical Society of America B 01/2013; 30:1092. · 2.18 Impact Factor
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ABSTRACT: We consider two entangled qubits, each of which is coupled to its own reservoir, so that their entanglement degrades with time. To enhance the qubits’ entanglement at a time during the evolution we propose a proper combination of pre- and postmeasurements to be performed locally on individual qubits. The premeasurements are weak measurements, but the postmeasurements may be either quantum measurement reversals or weak measurements again, depending on the situation at the time they are applied. Given the parameters of the initial qubits’ state, the premeasurements’ strength, and the evolution time, we establish the optimal conditions for the postmeasurements so that the qubits’ entanglement becomes the largest possible. Actually, by our scheme, less entangled qubits can evolve into more entangled ones with a finite probability, or even into a near-maximally entangled state but with a vanishingly low probability. We also examine the entanglement distribution among different pairs of subsystems involved and find out that the pairwise concurrence dynamics in our scheme differs strikingly from that in the situation without any control actions.
Phys. Rev. A. 11/2012; 86(5).
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ABSTRACT: We investigate the quantum interference induced by a relative phase in the
correlated initial state of a system which consists in a two-level atom
interacting with a damped mode of the radiation field. We show that the initial
relative phase has significant effects on both the evolution of the atomic
excited-state population and the information flow between the atom and the
reservoir, as quantified by the trace distance. Furthermore, by considering two
two-level atoms interacting with a common damped mode of the radiation field,
we highlight how initial relative phases can affect the subsequent entanglement
dynamics.
07/2012;
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ABSTRACT: We investigate the possibility and conditions to factorize the entanglement
evolution of a multiqubit system passing through multi-sided noisy channels. By
means of a lower bound of concurrence (LBC) as entanglement measure, we derive
an explicit formula of LBC evolution of the N-qubit generalized
Greenberger-Horne-Zeilinger (GGHZ) state under some typical noisy channels,
based on which two kinds of factorizing conditions for the LBC evolution are
presented. In this case, the time-dependent LBC can be determined by a product
of initial LBC of the system and the LBC evolution of a maximally entangled
GGHZ state under the same multi-sided noisy channels. We analyze the realistic
situations where these two kinds of factorizing conditions can be satisfied. In
addition, we also discuss the dependence of entanglement robustness on the
number of the qubits and that of the noisy channels.
05/2012;
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ABSTRACT: Addressing various types of decoherence is of paramount importance for employing entanglement in
quantum information processing and quantum computing. In this paper, we propose two schemes to manipulate
entanglement of two qubits stored in a common environment by means of combined weak measurements and
quantum measurement reversals. We derive the explicit conditions for the measurement strengths under which
at any time and for any initial states the qubits’ entanglement can be protected quite well with a reasonable finite
success probability. Moreover, the two schemes enable us in principle to achieve the maximal entanglement or
to restore the initial state (entanglement) of the qubits.
Physical Review A 01/2012; 86:012325. · 2.88 Impact Factor
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[show abstract]
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ABSTRACT: We consider two entangled qubits, each of which is coupled to its own reservoir, so that their entanglement
degrades with time. To enhance the qubits’ entanglement at a time during the evolution we propose a proper
combination of pre- and postmeasurements to be performed locally on individual qubits. The premeasurements
are weak measurements, but the postmeasurements may be either quantum measurement reversals or weak
measurements again, depending on the situation at the time they are applied. Given the parameters of the initial
qubits’ state, the premeasurements’ strength, and the evolution time, we establish the optimal conditions for the
postmeasurements so that the qubits’ entanglement becomes the largest possible. Actually, by our scheme, less
entangled qubits can evolve into more entangled ones with a finite probability, or even into a near-maximally
entangled state but with a vanishingly low probability. We also examine the entanglement distribution among
different pairs of subsystems involved and find out that the pairwise concurrence dynamics in our scheme differs
strikingly from that in the situation without any control actions.
Physical Review A 01/2012; 86:052322. · 2.88 Impact Factor
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ABSTRACT: We investigate the roles of different environmental models on quantum
correlation dynamics of two-qubit composite system interacting with two
independent environments. The most common environmental models (the
single-Lorentzian model, the squared-Lorentzian model, the two-Lorentzian model
and band-gap model) are analyzed. First, we note that for the weak coupling
regime, the monotonous decay speed of the quantum correlation is mainly
determined by the spectral density functions of these different environments.
Then, by considering the strong coupling regime we find that, contrary to what
is stated in the weak coupling regime, the dynamics of quantum correlation
depends on the non-Markovianity of the environmental models, and is independent
of the environmental spectrum density functions.
11/2011;
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ABSTRACT: In this work, we study the dynamics of quantum correlation (QC) in terms of quantum discord and its transfer for multiqubit systems in dissipative environments. At first, we investigate the dynamics of bipartite QC contained in a three-qubit system that are initially prepared in an extended W-like state with each qubit coupled to an independent reservoir. Subsequently, we study a realistic quantum network of several remote nodes each of which contains two qubits in contact with a common reservoir. For the simplest case of two nodes, we study the dynamics of QC and its transfer from the initially correlated system to the reservoirs and other degrees of freedom. In both models, we pay particular attention to the independent evolution and transfer of QC without the participation of entanglement when the systems of interest are initially prepared in unentangled states. We also observe the occurrence of sudden changes of quantum discord when the systems are initially in mixed states.
Journal of Physics B Atomic Molecular and Optical Physics 04/2011; 44(9):095504. · 1.88 Impact Factor
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ABSTRACT: We analyse the roles of initial correlations between a two-qubit system and a dissipative cavity on quantum discord dynamics of two qubits. Considering two initial system–cavity states, we find that the initial system–cavity correlations not only initially increase the two-qubit quantum discord but also lead to a larger long-time quantum discord asymptotic value. Moreover, quantum discord due to initial correlations is more robust than the case of the initial factorized state. Finally, we show the initial correlations' importance for dynamic behaviour of mutual information and classical correlation.
Journal of Physics B Atomic Molecular and Optical Physics 01/2011; 44(3):035503. · 1.88 Impact Factor
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ABSTRACT: We theoretically analyze the roles of initial correlations between a two-qubit system and a structured environment on entanglement dynamics of these two qubits. Considering two initial system-environment correlations, we show that the system-environment quantum correlation can initially increase the two-qubit entanglement, and the system-environment classical correlation would lead to the initially decreased two-qubit entanglement. Different two-qubit entanglement dynamics can be induced by these two initial system-environment correlations. However, under a certain condition, the roles of these two initial system-environment correlations on the two-qubit entanglement are the same.
Phys. Rev. A. 08/2010; 82(2).
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ABSTRACT: We analyze the roles of initial correlations between the two-qubit system and a dissipative cavity on quantum discord dynamics of two qubits. Considering two initial system-cavity states, we show that the initial system-cavity correlations not only can initially increase the two-qubit quantum discord but also would lead to a larger long-time quantum discord asymptotic value. Moreover, quantum discord due to initial correlations is more robust than the case of the initial factorized state. Finally, we show the initial correlations' importance for dynamics behaviors of mutual information and classical correlation.
07/2010;
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ABSTRACT: We consider the entanglement dynamics of N qubits interacting with independent structured reservoirs. The system is initially prepared in the multipartite Greenberger–Horne–Zeilinger (GHZ)-type state. We study the dependence of the entanglement dynamics on both the qubit number N and the purity of initial state, and show that the qubit number N and the purity can control the time of appearance of the N-qubit entanglement sudden death and the entanglement sudden birth of the reservoirs. Also based on the purity and the qubit number N, the revival of N-qubit entanglement does not necessarily indicate the disentanglement of reservoirs, and manifests before, simultaneously or even after the finite-time disentanglement of reservoirs.
Journal of Physics B Atomic Molecular and Optical Physics 01/2010; 43(4):045502. · 1.88 Impact Factor
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ABSTRACT: In this paper, we first present a simple measure for multiqubit entanglement based on the strategy of bipartite cuts and the measure of negativity. Then, we establish generalized monogamy inequalities and associated partition-dependent residual entanglement (PRE) accounting for arbitrary partitions of a multiqubit system. By virtue of the defined quantities, we investigate the entanglement dynamics of a system of N qubits, either in the Greenberger–Horne–Zeilinger (GHZ)-type state or in the W state, interacting with N independent reservoirs in both Markovian and non-Markovian regimes. We observe entanglement revivals of qubits at instantaneous points of disappearance or after a finite interval of abrupt vanishing due to the memory effect of non-Markovian reservoirs. We also follow the whole entanglement evolution in terms of the PRE to demonstrate the process of transition between the bipartite entanglement of all possible bipartitions and the multipartite entanglement. In particular, we show that the change in time of entanglement formats differs qualitatively for the GHZ-type and W states.
New Journal of Physics. 01/2010; 12:33020-17.
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ABSTRACT: In this paper, we first present a simple measure for multiqubit
entanglement based on the strategy of bipartite cuts and the measure of
negativity. Then, we establish generalized monogamy inequalities and associated
partition-dependent residual entanglement (PRE) accounting for arbitrary
partitions of a multiqubit system. By virtue of the defined quantities, we
investigate the entanglement dynamics of a system of N qubits, either in the
Greenberger–Horne–Zeilinger (GHZ)-type state or in the W state, interacting
with N independent reservoirs in both Markovian and non-Markovian regimes.
We observe entanglement revivals of qubits at instantaneous points of
disappearance or after a finite interval of abrupt vanishing due to the memory
effect of non-Markovian reservoirs. We also follow the whole entanglement
evolution in terms of the PRE to demonstrate the process of transition between
the bipartite entanglement of all possible bipartitions and the multipartite
entanglement. In particular, we show that the change in time of entanglement
formats differs qualitatively for the GHZ-type and W states.
New Journal of Physics 01/2010; 12:033020. · 4.18 Impact Factor
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ABSTRACT: A double Tavis-Cummings model (DTCM) is developed to simulate the entanglement dynamics of realistic quantum information processing where two entangled atom-pairs $AB$ and $CD$ are distributed in such a way that atoms $AC$ are embedded in a cavity $a$ while $BD$ are located in another remote cavity $b$. The evolutions of different types of initially shared entanglement of atoms are studied under various initial states of cavity fields. The results obtained in the DTCM are compared with that obtained in the double Jaynes-Cummings model (DJCM) [J. Phys. B \textbf{40}, S45 (2007)] and an interaction strength theory is proposed to explain the parameter domain in which the so-called entanglement sudden death occurs for both the DTCM and DJCM. Comment: 11 figures
02/2009;
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ABSTRACT: Entanglement dynamics of two atomic W-like states is studied within the framework of a triple Jaynes–
Cummings model. It is shown that the two states, though initially being equivalent under simple local operations
and thus having the same amounts of pairwise entanglements, undergo qualitatively different evolutions.
Namely, one of them may suffer from the so-called entanglement sudden death depending on the parameters,
while the other one does not for whatever parameters.
Journal of Modern Optics 01/2009; 56:1022. · 1.17 Impact Factor
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ABSTRACT: We investigate the disentanglement dynamics of generalized multiqubit Greenberger-Horne-Zeilinger-type states ∣Ψn,N⟩=α∣1⟩⊗n∣0⟩⊗(N−n)+β∣0⟩⊗n∣1⟩⊗(N−n) (with 1⩽n<N) in a local decoherence environment. By adopting the time after which all the bipartite entanglements vanish or become negligibly small as the criterion of entanglement robustness, we show that states ∣Ψn,N⟩ are more robust than states ∣ΨN⟩=α∣0⟩⊗N+β∣1⟩⊗N in all respects. Since the two states ∣ΨN⟩ and ∣Ψn,N⟩ can be transformed into each other by local operations, we confirm that entanglement robustness can be enhanced by local operations though the amount of entanglement cannot.
Phys. Rev. A. 11/2008; 78(6).
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ABSTRACT: We study the entanglement dynamics of strongly driven atoms off-resonantly coupled with cavity fields. We consider conditions characterized not only by the atom-field coupling but also by the atom-field detuning. By studying two different models within the framework of cavity QED, we show that the so-called atomic entanglement sudden death (ESD) always occurs if the atom-field coupling lager than the atom-field detuning, and is independent of the type of initial atomic state.
11/2008;
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ABSTRACT: We study entanglement dynamics for a six-qubit model in cavity QED, where three two-level atoms A, B and C are initially prepared in a Greenberger–Horne–Zeilinger (GHZ)-like state and locally coupled with the independent cavities a, b and c, respectively. We consider entanglement evolution via negativity for the tripartite subsystems of atoms and the corresponding cavities. By choosing two types of GHZ-like states as atomic initial states, we shall show that the entanglement of atoms may or may not exhibit entanglement sudden death (ESD) depending on the type of atomic initial state.
Journal of Physics B Atomic Molecular and Optical Physics 07/2008; 41(15):155501. · 1.88 Impact Factor
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ABSTRACT: In this paper, we study the entanglement dynamics of atoms coupled to cavity fields. We consider conditions characterized not only by the purity of the atomic initial state but also by the cavity photon number. By studying three different models within the framework of cavity QED, we show that the so-called atomic entanglement sudden death always occurs if initially the atomic state is sufficiently impure and/or the cavity photon number is nonzero.
Journal of Physics B Atomic Molecular and Optical Physics 04/2008; 41(8):085503. · 1.88 Impact Factor
