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1.
The entanglement of two atomic qubits, which are coupled to a coherent state field with different couplings, is studied. The dynamical evolution of the concurrence, which measures the degree of the entanglement between the two qubits, is plotted versus the scaled
time gt. It is found that the two qubits can be entangled by the coherent state field even when they are initially prepared in the most mixed state, and for very weak field, the most mixed state can be more easily entangled than some pure
states. It is also found that the entanglement between the qubits sensitively depends on the relative difference of the atomic couplings and the mean photon number of the field. 相似文献
2.
We study the entanglement properties of a class of N-qubit quantum states that are generated in arrays of qubits with an Ising-type interaction. These states contain a large amount of entanglement as given by their Schmidt measure. They also have a high persistency of entanglement which means that approximately N/2 qubits have to be measured to disentangle the state. These states can be regarded as an entanglement resource since one can generate a family of other multiparticle entangled states such as the generalized Greenberger-Horne-Zeilinger states of 相似文献
3.
Considering the generalized double Jaynes-Cummings model, we examine the entanglement between two non-identical dipole-dipole coupled qubits interacting with two independent detuned vacuum cavity modes. We calculate the negativity as a measure of qubits entanglement. We find that entanglement parameter evolve periodically with time and the period are affected by the model parameters and initial states of qubits. For unentangled initial states the detuning and dipole-dipole interaction affect only the period of entanglement oscillations, not the maximum value of entanglement. For entangled states the detuning stabilizes the entanglement parameter oscillations. According to choice of initial entangled state the dipole-dipole strength is greatly enhances or weakens the oscillations of the entanglement parameter. 相似文献
4.
We study the entanglement dynamics of three qubits in
contact with independent Markovian or non-Markovian reservoirs. The
qubits are prepared in two types of GHZ-like or W-like states
distinguished by initial excited-state populations. Though belonging
to the same GHZ or W class of entanglement, the states with
different initial excitations exhibit strikingly different dynamics.
In addition, we show that the non-Markovian reservoirs can recover
the multiqubit entanglement at instantaneous points or after a
finite interval of entanglement disappearance. We also investigate
the protection of multiqubit entanglement by the control of
excitation emission via the detuning. 相似文献
5.
We analyze a controllable generation of maximally entangled mixed states of
a circuit containing two-coupled superconducting charge qubits. Each qubit
is based on a Cooper pair box connected to a reservoir electrode through a
Josephson junction. Illustrative variational calculations were performed to
demonstrate the effect on the two-qubits entanglement. At sufficiently
deviation between the Josephson energies of the qubits and/or strong
coupling regime, maximally entangled mixed states at certain instances of
time is synthesized. We show that entanglement has an interesting subsequent
time evolution, including the sudden death effect. This enables us to
completely characterize the phenomenon of entanglement sharing in the
coupling of two superconducting charge qubits, a system of both theoretical
and experimental interest. 相似文献
6.
Using the method of the Jordan--Wigner transformation for solving
different spin--spin correlation functions, we have investigated the
generation of next-nearest-neighbouring entanglement in a
one-dimensional quantum Ising spin chain with the Gaussian
distribution impurities of exchange couplings and external magnetic
fields taken into account. The maximal value of entanglement
between the next-nearest-neighbouring qubits in the transverse Ising
model was analysed in detail by varying the effectively controlled
parameters such as interchange coupling, magnetic field and the
system impurity. For such systems, where both exchange couplings and
external magnetic field disorder appear, we show that it is possible
to achieve next-nearest-neighbouring entanglement better than the
previously discussed pure Ising spin chain case. We also show that
the Gaussian distribution impurity can induce
next-nearest-neighbouring entanglement, which can be used as a means
to characterize quantum phase transition. 相似文献
7.
We investigate the time evolution of entanglement for bipartite systems of
arbitrary dimensions under the influence of decoherence. For qubits, we
determine the precise entanglement decay rates under different
system-environment couplings, including finite temperature effects. For qudits, we show how
to obtain upper bounds for the decay rates and also present exact solutions
for various classes of states. 相似文献
9.
Two charge qubits being coupled to a damped cavity with different couplings are considered. The dynamical evolution of the entanglement between the two qubits is demonstrated analytically or numerically. It is found that with the cavity dissipation, the steady entanglement between the two qubits can be achieved. The two qubits being initially in the separable and most mixed state can be easily induced to a steady entangled state, and the relative difference of the couplings can be used to enhance the steady entanglement between the two charge qubits. 相似文献
10.
A theoretical scheme for the generation of maximally entangled states of two superconducting flux qubits via their sequential interaction with a monochromatic quantum field is presented. The coupling of the qubits with the quantized field can be tuned on and off resonance by modulating the effective Josephson energy of each qubit via an externally applied magnetic flux. The system operates in such a way as to transfer the entanglement from a bipartite field-qubit subsystem to the two qubits. This scheme is attractive in view of the implementation of practical quantum processing systems. 相似文献
11.
We study the interaction between a single-mode quantized field and a quantum system composed of two qubits. We suppose that two qubits initially be prepared in the mixed and separable state, and study how entanglement between two qubits arises in the course of evolution according to the Jaynes-Cummings type interaction with nonclassical radiation field. We also investigate the relation between entanglement and purity of qubit subsystem. We show that different photon statistics have different effects on the dynamical behavior of the qubit subsystem. When the qubits are initially prepared in the maximally mixed and separable state, for coherent state field we cannot find entanglement between two qubits; for squeezed state field entanglement between two qubits exists in several short period of time; for even and odd coherent state fields of large photon number, the dynamical behavior of the entanglement between two qubits shows collapse and revival phenomenon. For odd coherent state field of small photon number, the entanglement with both qubits initially prepared in maximally mixed state can be stronger than that with both qubits initially prepared in pure states. For fields of small photon number, the entanglement strongly depends on the states they are initially prepared in. For coherent state field, and odd and even coherent state fields of large photon number, the entanglement only depends on the purity of the initial state of qubit subsystem. We also show that during the evolution the unentangled state may be purer than the entangled state, and the maximum degree of entanglement may not occur at the time when the qubit subsystem is in the purist state. 相似文献
12.
We study the interaction between a single-mode quantized field and a quantum system composed of two qubits. We suppose that two qubits initially be prepared in the mixed and separable state, and study how entanglement between two qubits arises in the course of evolution according to the Jaynes-Cummings type interaction with nonclassical radiation field. We also investigate the relation between entanglement and purity of qubit subsystem. We show that different photon statistics have different effects on the dynamical behavior of the qubit subsystem. When the qubits are initially prepared in the maximally mixed and separable state, for coherent state field we cannot find entanglement between two qubits; for squeezed state field entanglement between two qubits exists in several short period of time; for even and odd coherent state fields of large photon number, the dynamical behavior of the entanglement between two qubits shows collapse and revival phenomenon. For odd coherent state field of small photon number, the entanglement with both qubits initially prepared in maximally mixed state can be stronger than that with both qubits initially prepared in pure states. For fields of small photon number, the entanglement strongly depends on the states they are initially prepared in. For coherent state field, and odd and even coherent state fields of large photon number, the entanglement only depends on the purity of the initial state of qubit subsystem. We also show that during the evolution the unentangled state may be purer than the entangled state, and the maximum degree of entanglement may not occur at the time when the qubit subsystem is in the purist state. 相似文献
13.
We consider a system of three uncoupled entangled qubits undergoing a decoherence process (DP) induced by a classical environmental noise portrayed by a Gaussian distributed fluctuating field with either Ornstein–Uhlenbeck (OU) or Gaussian (G) autocorrelation function. The impacts of such a DP on the entanglement of the qubits are analyzed in detail when they are initialized either in the GHZ- or W-type states and interact with the fluctuating field in three different scenarios namely, common, independent and mixed environment(s). We found that: (i) the way the qubits interact with the noise as well as their initial state play an important role towards the protection of entanglement; (ii) there are optimal parameters which permit to delay or totally avoid the disentanglement of the qubits; (iii) irrespective of the qubit-noise coupling (QNC) scenario and the initial prepared state considered, the OU noise is more injurious to the survivorship of entanglement than the G one. Specifically, we show that, irrespective of the QNC scenario and the character of the noise considered, the DP disentangles the qubits more quickly when they are initialized in the W-type states than in the GHZ-type one. Furthermore, we show that when the initial state of the qubits is considered to be a W-type state, the disentanglement occurs more rapidly in the common environment (CE) scenario followed by the mixed environments (MEs) scenario than in the independent environments (IEs) one. However, the situation is completely reversed when a GHZ-type state is considered. 相似文献
14.
We show that a high degree of steady-state entanglement between two spatially separated and initially uncoupled qubits can be achieved via interaction with a quantized squeezed field in a cavity. The cavity field induces two-photon coherence, which is crucial in creating entanglement between the qubits. Optimum entanglement is obtained when the less dissipative qubit is incoherently pumped while the other dissipates the excitation. Given the current state-of-the-art in cavity quantum electrodynamics and squeezed light sources, our scheme presents an effective way for light-to-matter entanglement transfer. 相似文献
15.
We study the manipulation of quantum entanglement by periodic external fields. As an entanglement measure we compute numerically the concurrence of two coupled superconducting qubits both driven by a dc + ac external control parameter. We show that when the driving term of the Hamiltonian commutes with the qubit–qubit interaction term, it is possible to create or destroy entanglement in a controlled way by tuning the system at or near multiphoton resonances. On the other hand, when the driving does not commute with the qubit–qubit interaction, the control and generation of entanglement induced by the driving field is more robust and extended in parameter space, beyond the multiphoton resonances. 相似文献
16.
We study the dynamics of multipartite entanglement under
decoherence induced by the environment consisting of a fermionic
bath. Based on the algebraic measure of entanglement-negativity, we analyze the time evolution of entanglement of both
pure states and mixed ones, and find that entanglement evolution
depends on both bath temperature and the number of qubits of
the system. A linear space S LDF which is dynamically decoupled
from the environment is identified in the sense of linear entropy
to symbolize the environment effect. 相似文献
17.
We propose a scheme to generate entanglement between two distant qubits(two-level atom) which are separately trapped in their own(in general) non-Markovian dissipative cavities by utilizing entangling swapping, considering the case in which the qubits can move along their cavity axes rather than a static state of motion. We first examine the role of movement of the qubit by studying the entropy evolution for each subsystem. The average entropy over the initial states of the qubit is calculated. Then by performing a Bell state measurement on the fields leaving the cavities, we swap the entanglement between qubit-field in each cavity into qubit-qubit and field-field subsystems. The entangling power is used to measure the average amount of swapped entanglement over all possible pure initial states. Our results are presented in two weak and strong coupling regimes, illustrating the positive role of movement of the qubits on the swapped entanglement.It is revealed that by considering certain conditions for the initial state of qubits, it is possible to achieve a maximally long-leaving stationary entanglement(Bell state) which is entirely independent of the environmental variables as well as the velocity of qubits. This happens when the two qubits have the same velocities. 相似文献
19.
Scalable quantum networks require the capability to create, store and distribute entanglement among distant nodes (atoms,
trapped ions, charge and spin qubits built on quantum dots, etc.) by means of photonic channels.
We show how the entanglement between qubits and electromagnetic field modes allows generation of entangled states of remotely
located qubits. We present analytical calculations of linear entropy and the density matrix for the entangled qubits for the
system described by the Jaynes-Cummings model. We also discuss the influence of decoherence. The presented scheme is able
to drive an initially separable state of two qubits into an highly entangled state suitable for quantum information processing. 相似文献
20.
Graph states are special multipartite entangled states that have been proven useful in a variety of quantum information tasks. We address the issue of characterizing and quantifying the genuine multipartite entanglement of graph states up to eight qubits. The entanglement measures used are the geometric measure, the relative entropy of entanglement, and the logarithmic robustness, have been proved to be equal for the genuine entanglement of a graph state. We provide upper and lower bounds as well as an iterative algorithm to determine the genuine multipartite entanglement. 相似文献
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