共查询到20条相似文献,搜索用时 15 毫秒
1.
We study the nonlocal correlations and quantum entanglement for two deformed bosonic fields of arbitrary deformation parameters, q 1 and q 2, prepared in an entanglement of deformed coherent states. As a measure of entanglement, we use the von Neumann entropy and investigate its behavior for different strength regimes of the optical fields. We find that the photon number can enhance the von Neumann entropy, and the deformation parameters can restrain the system entanglement. 相似文献
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Pradip Laha B. Sudarsan S. Lakshmibala V. Balakrishnan 《International Journal of Theoretical Physics》2016,55(9):4044-4059
A Λ-type atom interacting with two radiation fields exhibits electromagnetically induced transparency and other nonclassical effects that appear in the entanglement dynamics of the atomic subsystem and in appropriate field observables. Both EIT and field-atom entanglement are important for quantum information processing. We investigate the roles played by specific initial field states, detuning parameters, field nonlinearities and intensity-dependent field-atom couplings on EIT and the entanglement between subsystems. Departure from coherence of the initial field states produces significant effects. We investigate these aspects in a model that exhibits the salient features of entangled tripartite systems. For initial photon-added coherent states, collapses and revivals of the atomic subsystem von Neumann entropy appear as the intensity parameter varies over a narrow range of values. These features could be useful in enabling entanglement. 相似文献
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R. Safaiee M. M. Golshan 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,83(4):457-463
The present work is concerned with an analysis of the entanglement between the electronic
coherent superpositions of spin states and subbands in a
quasi-one-dimensional Rashba nanoloop acted upon by a strong perpendicular magnetic field.
We explicitly include the confining potential and the Rashba spin-orbit coupling into the
Hamiltonian and then proceed to calculate the von Neumann entropy, a measure of
entanglement, as a function of time. An analysis of the von Neumann entropy demonstrates
that, as expected, the dynamics of entanglement strongly depends upon the initial state
and electronic subband excitations. When the initial state is a pure one formed by a
subband excitation and the z-component of spin states, the entanglement exhibits periodic
oscillations with local minima (dips). On the other hand, when the initial state is formed
by the subband states and a coherent superposition of spin states, the
entanglement still periodically oscillates, exhibiting stronger correlations, along with
elimination of the dips. Moreover, in the long run, the entanglement for the latter case
undergoes the phenomenon of collapse-revivals. This behaviour is absent for the first case
of the initial states. We also show that the degree of entanglement strongly depends upon
the electronic subband excitations in both cases. 相似文献
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This paper investigates the entanglement in the supermolecular dimer [Mn4]2 consisting of a pair of single molecular magnets with antiferromagnetic exchange-coupllng J. The conventional yon Neumann entropy as a function of the exchange-coupling is calculated explicitly for all eigenstates with the quantum number range from M = M1 + M2 = -9 to 0. It is shown that the yon Neumann entropy is not a monotonic function of the coupling strength. However, it is significant that the entropy of entanglement has the maximum values and the minimum values for most eigenstates, which is extremely useful in the quantum computing. It also presents the time-evolution of entanglement from various initial states. The results are useful in the design of devices based on the entanglement of two molecular magnets. 相似文献
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增光子二模纠缠相干态的纠缠特性及其通过腔量子电动力学的制备 总被引:2,自引:1,他引:1
分析了增光子二模纠缠相干态的纠缠特性,得到共生纠缠度的解析表示式.结果表明:增光子二模纠缠相干态的共生纠缠度与叠加态的相位有非常灵敏的关系.提出了一种制备增光子相干态和增光子二模纠缠相干态的方法,其制备过程为首先把增光子相干态转化为相干态与真空态一种特殊的叠加态(叠加系数与相干态振幅有关),再通过位于高Q腔内的原子与经典激光场的相互作用,从而实现增光子相干态的制备.通过一个飞行原子先后与两个光腔中光场相互作用可以实现增光子二模纠缠相干态的制备. 相似文献
8.
Rosa Safaiee Mohammad Mehdi Golshan 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(6):121
The main purpose of the present article is to report the characteristics of von Neumann entropy, thereby, the electronic hybrid entanglement, in the heterojunction of two semiconductors, with due attention to the Rashba and Dresselhaus spin-orbit interactions. To this end, we cast the von Neumann entropy in terms of spin polarization and compute its time evolution; with a vast span of applications. It is assumed that gate potentials are applied to the heterojunction, providing a two dimensional parabolic confining potential (forming an isotropic nanodot at the junction), as well as means of controlling the spin-orbit couplings. The spin degeneracy is also removed, even at electronic zero momentum, by the presence of an external magnetic field which, in turn, leads to the appearance of Landau states. We then proceed by computing the time evolution of the corresponding von Neumann entropy from a separable (spin-polarized) initial state. The von Neumann entropy, as we show, indicates that electronic hybrid entanglement does occur between spin and two-dimensional Landau levels. Our results also show that von Neumann entropy, as well as the degree of spin-orbit entanglement, periodically collapses and revives. The characteristics of such behavior; period, amplitude, etc., are shown to be determined from the controllable external agents. Moreover, it is demonstrated that the phenomenon of collapse-revivals’ in the behavior of von Neumann entropy, equivalently, electronic hybrid entanglement, is accompanied by plateaus (of great importance in quantum computation schemes) whose durations are, again, controlled by the external elements. Along these lines, we also make a comparison between effects of the two spin-orbit couplings on the entanglement (von Neumann entropy) characteristics. The finer details of the electronic hybrid entanglement, which may be easily verified through spin polarization measurements, are also accreted and discussed. The novel results of the present article, with potent applications in the field of quantum information processing, provide a deeper understanding of the electronic von Neumann entropy and hybrid entanglement that occurs in two-dimensional nanodots. 相似文献
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Xi-Wen Hou Ming-Fang Wan Zhong-Qi Ma 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,62(2):279-288
Various measures of entanglement have triggered considerable interest in the
relationship between entanglement measures and other
well-known quantities. As a demonstration, the dynamical
correlation of negativity and entropy is studied in two
coupled quartic oscillators for initial pure and mixed states that
are respectively taken to be the products and mixed density
matrices of coherent states and squeezed states on each
oscillator. The correlation with energy is also considered.
It is shown that for the initial pure states with a
small magnitude, two negativities are
positively correlated with the von Neumann entropy while they are anti-correlated with
the energy of each oscillator in the weak coupling regime. For mixed states
with a small magnitude the two negativities and the mutual entropy exhibit dominantly
positive correlation, whereas those three quantities are
dominantly anti-correlated with the sum of energies of two
oscillators in the case of weak interactions. Such correlation behaviors in the mixed
state with small magnitudes are most striking at the same step in
maximal and minimal values and in oscillation. The differences in
entropies and negativities between coherent states and squeezed
states are discussed. These are useful for quantum
entanglement and quantum information processing. 相似文献
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An entanglement measure for multipartite pure states is formulated using the product of the von Neumann entropy of the reduced
density matrices of the constituents. Based on this new measure, all possible ways of the maximal entanglement of the triqubit
pure states are studied in detail and all types of the maximal entanglement have been compared with the result of ‘the average
entropy’. The new measure can be used to calculate the degree of entanglement, and an improvement is given in the area near
the zero entropy. 相似文献
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It is emphasized that quantum entanglement determined in terms of the von Neumann entropy operator is a stochastic quantity
and, therefore, can fluctuate. The rms fluctuations of the entanglement entropy of two-qubit systems in both pure and mixed
states have been obtained. It has been found that entanglement fluctuations in the maximally entangled states are absent.
Regions where the entanglement fluctuations are larger than the entanglement itself (strong fluctuation regions) have been
revealed. It has been found that the magnitude of the relative entanglement fluctuations is divergent at the points of the
transition of systems from an entangled state to a separable state. It has been shown that entanglement fluctuations vanish
in the separable states. 相似文献
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The entanglement dynamics of two vibrational modes of a polyatomic molecule coupled by Coriolis interaction to overall molecular rotation is studied in terms of two negativities, N(t) and Ns(t), respectively, defined by the minimum of the eigenvalues and by the sum of the negative eigenvalues of the partial transpose of a density matrix. Various initial states are the products of Dicke states and the products of coherent states of vibrations and rotations. Formaldehyde is taken as an example, and the von Neumann entropy s(t) is simulated for the comparison with both negativities. It is shown that negativity Ns(t) is positively correlated with entropy s(t), and the correlated behavior between negativity N(t) and entropy s(t) strongly depends on initial states. However, these three indicators of entanglement display a dominantly positive correlation for the coherent states with small or large parameters. In addition, for the latter state two quantities N(t) and s(t) are nearly unchanged for a long time. This time can be further increased by the increasing of vibrational quantum number so that molecular information processing and quantum computing is allowed. These results are useful in quantum information theory. 相似文献
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本文利用相干态正交化展开方法, 对两格点两电子Hubbard-Holstein极化子模型的能谱以及动力学特性进行了精确求解. 讨论了耦合强度g、平均声子数n以及电子 初态对纠缠演化特性及系统冯诺依曼熵的影响. 数值计算结果表明: 1)纠缠度随时间的演化呈现出良好的周期性, 当其他的参数固定时, 演化周期随耦合强度g增大逐渐减小, 与平均声子数n无关; 2)系统冯诺依曼熵同电子状态占有率表现出严格的同步演化特性; (3) 在弱耦合强度和低平均声子数下, 初始电子态c2↑+ c2↓+|O>e或c1↑+ c1↓+ |O>e较c1↑+c2↓+—c1↓+ c2↑+具有更大的最大冯诺依曼熵, 并随耦合强度增大、平均声子数的增加而逐渐接近. 相似文献
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Jing Zhang 《Optics Communications》2007,277(2):353-358
As an important parameter, von Neumann entropy has been used to characterize the entanglement between atom and light field. We discussed the entanglement and nonclassicality evolution of an atom in a squeezed vacuum—a typical nonclassical field, and compare it with that of the coherent state. It shows that the atom-field entanglement in squeezed vacuum is much stronger and stabler than that in coherent state, whereas the nonclassicality of the light field depends on its initial status. This investigation is trying to find a new insight into the relation between entanglement of atom-field system and nonclassicality of light fields. The result shows that the entanglement between the atom and the field can be maintained well in the squeezed vacuum and this implies better control of atom and photon mutually. 相似文献
17.
Andreas Winter 《Communications in Mathematical Physics》2016,347(1):291-313
We present a bouquet of continuity bounds for quantum entropies, falling broadly into two classes: first, a tight analysis of the Alicki–Fannes continuity bounds for the conditional von Neumann entropy, reaching almost the best possible form that depends only on the system dimension and the trace distance of the states. Almost the same proof can be used to derive similar continuity bounds for the relative entropy distance from a convex set of states or positive operators. As applications, we give new proofs, with tighter bounds, of the asymptotic continuity of the relative entropy of entanglement, ER, and its regularization \({E_R^{\infty}}\), as well as of the entanglement of formation, EF. Using a novel “quantum coupling” of density operators, which may be of independent interest, we extend the latter to an asymptotic continuity bound for the regularized entanglement of formation, aka entanglement cost, \({E_C=E_F^{\infty}}\). Second, we derive analogous continuity bounds for the von Neumann entropy and conditional entropy in infinite dimensional systems under an energy constraint, most importantly systems of multiple quantum harmonic oscillators. While without an energy bound the entropy is discontinuous, it is well-known to be continuous on states of bounded energy. However, a quantitative statement to that effect seems not to have been known. Here, under some regularity assumptions on the Hamiltonian, we find that, quite intuitively, the Gibbs entropy at the given energy roughly takes the role of the Hilbert space dimension in the finite-dimensional Fannes inequality. 相似文献
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In this work, we present an investigation on the spatial entanglement entropies in the helium atom by using highly correlated Hylleraas functions to represent the S-wave states. Singlet-spin 1sns 1 S e states (with n = 1 to 6) and triplet-spin 1sns 3 S e states (with n = 2 to 6) are investigated. As a measure on the spatial entanglement, von Neumann entropy and linear entropy are calculated. Furthermore, we apply the Schmidt–Slater decomposition method on the two-electron wave functions, and obtain eigenvalues of the one-particle reduced density matrix, from which the linear entropy and von Neumann entropy can be determined. 相似文献
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Quantum entanglement of two stretches in molecule H2S is investigated for various initial states in terms of the reduced-density yon Neumann entropy and the mean entropy defined by average over time. It is shown that the maximal and the mean entropies of an initial state with local-mode character are smaller than those with normal-mode character, and the mean entropy displays a maximum near the position of the normal-to-local transition. 相似文献