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1.
Vlatko Vedral 《Central European Journal of Physics》2003,1(2):289-306
We study properties of entangled systems in the (mainly non-relativistic) second quantization formalism. This is then applied
to interacting and non-interacting bosons and fermions and the differences between the two are discussed. We present a general
formalism to show how entanglement changes with the change of modes of the system. This is illustrated with examples such
as the Bose condensation and the Unruh effect. It is then shown that a non-interacting collection of fermions at zero temperature
can be entangled in spin, providing that their distances do not exceed the inverse Fermi wavenumber. Beyond this distance
all bipartite entanglement vanishes, although classical correlations still persist. We compute the entanglement of formation
as well as the mutual information for two spin-correlated electrons as a function of their distance. The analogous, non-interacting
collection of bosons displays no entanglement in the internal degrees of freedom. We show how to generalize our analysis of
the entanglement in the internal degrees of freedom to an arbitrary number of particles. 相似文献
2.
3.
研究了一维三量子比特海森伯模型中的对纠缠的提高和控制问题,在该系统中引入了Dzyaloshinskii-Moriya(DM)相互作用,通过求解共生来计算两量子比特之间的热纠缠,结果表明:对于XXX模型,引入DM相互作用D,可以诱导铁磁和反铁磁自旋链产生热纠缠,尽管它们产生热纠缠所需的D值大小不同.对于XXZ模型,引入DM相互作用后,可以使原本不存在热纠缠的反铁磁自旋链产生纠缠,而且对于铁磁和反铁磁这两种XXZ自旋链,DM相互作用和各向异
关键词:
纠缠
XXX模型')" href="#">XXX模型
XXZ模型')" href="#">XXZ模型
Dzyaloshinskii-Moriya相互作用 相似文献
4.
应用Von Neumann熵和Schmid tnumber K两种纠缠度量讨论了各向异性光子晶体中二能级原子和自发辐射场间纠缠度的演化性质.研究发现,原子-光场纠缠度的演化与原子上能级和光子晶体能带带边的相对位置有关,当原子上能级处于光子晶体禁带内,原子-光场纠缠度将保持稳定,当原子上能级处于光子晶体能带中,原子-光场纠缠度先增大后衰减到零.纠缠度的大小还与原子的初态有关.可以通过控制原子的初态和原子上能级与带边的相对位置来控制原子-光场纠缠度的演化特性. 相似文献
5.
研究了初态为X态时Tavis-Cummings模型中具有偶极相互作用两原子的纠缠演化特性,在演化过程中,同时号码出现了两原子的纠缠突然死亡(ESD)与突然产生(ESB)两种有趣的现象.详细分析了两原子初始态的纯度、偶极相互作用、光场粒子数对这两种现象出现时间的影响,进一步给出了初始为混态时ESB与ESD的转换条件.计算结果表明,上述系统参量对两原子的纠缠演化、ESB与ESD有重要的影响,偶极相互作用会改变纠缠度的振荡周期,使出现ESD的时间间隔减少;随着初始两原子纠缠纯度的增大,纠缠突然产生以及纠缠突然死亡存在的时间缩短,并且可以提高两原子之间的纠缠;对于特殊的初态,产生了纠缠不变性以及固定的两原子纠缠,该定值受两原子初始状态的纯度控制。 相似文献
6.
Pawel Horodecki 《Central European Journal of Physics》2003,1(4):695-707
We consider the problem of invariance of distillable entanglement D and quantum capacities Q under erasure of information about single copy of quantum state or channel respectively. We argue that any 2 ⊗N two-way distillable state is still two-way distillable after erasure of single copy information. For some known distillation
protocols the obtained two-way distillation rate is the same as if Alice and Bob knew the state from the very beginning. The
isomorphism between quantum states and quantum channels is also investigated. In particular it is pointed out that any transmission
rate down the channel is equal to distillation rate with formal LOCC-like superoperator that uses in general nonphysical Alice
actions. This allows to we prove that if given channel Λ has nonzero capacity (Q
→ or Q
⟺) then the corresponding quantum state ϱ(Λ) has nonzero distillable entanglement (D
→ or D
⟺). Follwoing the latter arguments are provided that any channel mapping single qubit into N level system allows for reliable two-way transmission after erasure of information about single copy. Some open problems
are discussed. 相似文献
7.
We present a discussion on local quantum correlations and their relations with entanglement. We prove that a vanishing coefficient
of quantum correlations implies separability. The new results on locally decomposable maps which we obtain in the course of
the proof also seem to be of independent interest. 相似文献
8.
This paper studies the discord of a bipartite two-level system coupling to an XY spin-chain environment in a transverse field and investigates the relationship between the discord property and the environment’s quantum phase transition.The results show that the quantum discord is also able to characterize the quantum phase transitions.We also discuss the difference between discord and entanglement,and show that quantum discord may reveal more general information than quantum entanglement for characterizing the environment’s quantum phase transition. 相似文献
9.
研究了Dzyaloshinskii-Moriya(DM)相互作用对混合自旋(1/2,3/2)XY链以及自旋为1的XY链热纠缠的影响.通过计算两粒子之间的纠缠,发现它不仅能够增强纠缠,而且能使两粒子之间的纠缠度达到一稳定值;当温度较高时,要使热纠缠达到稳定值需要更强的这种相互作用.在相同的条件下,自旋s=1的两粒子之间的纠缠要小于混合自旋两粒子之间的纠缠.粒子之间的交换耦合相互作用有助于加强粒子之间的热纠缠,因此可以与DM相互作用一起调节纠缠度.当交换耦合相互作用比
关键词:
量子纠缠
XY 模型')" href="#">XY 模型
negativity
Dzyaloshinskii-Moriya相互作用 相似文献
10.
11.
12.
Recep Eryi?it 《International Journal of Theoretical Physics》2009,48(3):885-893
We have analyzed the behavior of multipartite global entanglement and average bipartite concurrence for the sign of quantum
phase transitions in the frustrated J
1−J
2 model by using exact diagonalization technique for a chain of 12 qubits. It is found that although the magnitude of two classes
of the measures show opposite trends the absolute value of their derivatives show similar structure near critical points. 相似文献
13.
研究四量子比特海森堡XXZ模型中配对纠缠的性质,在该系统中引入了Dzyaloshinskii-Moriya (DM)相互作用,通过求解配对纠缠度来讨论最近邻和次近邻两量子比特之间的热纠缠性质. 研究结果表明:对于铁磁和反铁磁两种情形而言,次近邻两量子比特之间不存在配对热纠缠;但在最近邻两量子比特情况时,DM相互作用和各向异性参数Δ对配对热纠缠和临界温度Tc都具有重要的影响,且随着温度T的增加,配对纠缠度逐渐减小直至消失. 因此,选择和调整合适的DM相互作用和各向异性参数,可以有效地控制和提高配对热纠缠.
关键词:
配对纠缠
XXZ模型')" href="#">XXZ模型
Dzyaloshinskii-Moriya相互作用 相似文献
14.
研究了一维随机量子XY自旋链中中心两量子位的纠缠特性,在该系统中引入了自旋间的交换耦合杂质、磁杂质和Dzyaloshinskii-Moriya相互作用,并且杂质满足高斯分布关系.通过数值计算,求出了自旋的关联函数和平均磁化强度,给出了Concurrence的解析表达式.结果表明:高斯分布和Dzyaloshinskii-Moriya相互作用对两量子位的纠缠有重要的影响,选择合适的交换耦合、外界磁场和Dzyaloshinskii-Moriya相互作用参数,可以控制和提高中心两量子位的纠缠.
关键词:
纠缠
XY模型')" href="#">随机量子XY模型
高斯分布
Dzyaloshinskii-Moriya相互作用 相似文献
15.
The evolution of the field entropy and the entanglement between the atom and the field for the system of a single-mode vacuum
field interacting with a Ξ-type three-level atom have been studied by using the reduced quantum entropy. The influences of the detuning of the light
field and the setting of the initial state of the atom on the field entropy and entanglement of the system under consideration
are discussed emphatically. It is showed that the detuning of the light field and the setting of the initial state of the
atom play an important role for the evolution of the field entropy and the entanglement between the atom and the field. The
general conclusions reached are illustrated by numerical results. 相似文献
16.
We derive explicit expressions for quantum discord and classical correlation for an X structure density matrix. Based on the characteristics of the expressions, the quantum discord and the classical correlation are easily obtained and compared under different initial conditions using a novel analytical method. We explain the relationships among quantum discord, classical correlation, and entanglement, and further find that the quantum discord is not always larger than the entanglement measured by concurrence in a general two-qubit X state. The new method, which is different from previous approaches, has certain guiding significance for analysing quantum discord and classical correlation of a two-qubit X state, such as a mixed state. 相似文献
17.
Teleportation and thermal entanglement in two-qubit Heisenberg X Y Z spin chain with the Dzyaloshinski-Moriya interaction and the inhomogeneous magnetic field 下载免费PDF全文
This paper studies the average fidelity of teleportation and thermal entanglement for a two-qubit Heisenberg X Y Z chain in the presence of both an inhomogeneous magnetic field and a Dzyaloshinski-Moriya interaction. It shows that for a fixed Dz, the increase of bz will broaden the critical temperature at the cost of decreasing the thermal entanglement. And it can modulate the inhomogeneous magnetic field and the Dzyaloshinski-Moriya interaction for the average fidelity of teleportation to be optimal. 相似文献
18.
A. N. Yakunin 《Central European Journal of Physics》2003,1(2):355-362
Based on a solution of the polymer excluded volume problem, a technique is proposed to estimate some parameters at the isotropic-nematic
liquid crystal phase transition (the product of the volume fraction of hard sticks and the ratio of the stick length, L, to its diameter, D; the maximum value of this ratio at which one cannot regard the stick as hard). The critical exponents are estimated. The
transition of a swelling polymer coil to ideal is revealed as the polymerization degree of a macromolecule increases. The
entanglement concentration obtained agrees with experimental data for polymers with flexible chains. The number of monomers
between neighbor entanglements is assumed to be the ratio L/D. A comparison of the theory with other ones and recent experimental data is made. 相似文献
19.
The characteristics of pairwise entanglement and local polarization (LP) are discussed by studying the ground state (states)
of the Heisenberg XX model. The results show that: the ground state (states) is (are) composed of the micro states with the minimal polarization
(0 for even qubit and 1/2 for odd qubit); LP and the probability of the micro state have an intimate relation, i.e. the stronger
the LP, the smaller the probability, and the same LP corresponds to the same probability; the pairwise entanglement of the
ground state is the biggest in all eigenvectors. It is found that the pairwise entanglement is decreased by the state degeneracy
and the system size. The concurrence approaches a fixed value of about 0.3412 (for odd-qubit chain) or 0.3491 (for even-qubit
chain) if the qubit number is large enough.
Supported by the National Natural Science Foundation of China (Grant Nos. 10547008, 90403034, 90403019, 90406017 and 60525417),
the National Key Basic Research Special Foundation of China (Grant Nos. 2005CB724508 and 2006CB921400), the Foundation of
Xi’an Institute of Post and Telecommunications (Grant No. 105-0414), and the Natural Science Foundation of Shanxi Province
(Grant No. 2004A15) 相似文献
20.
J. S. Zhang J. B. Xu Q. Lin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(2):283-288
We investigate the entanglement dynamics of a quantum system consisting of two-level atoms interacting with vacuum or thermal
fields with classical driving fields. We find that the entanglement of the system can be improved by adjusting the classical
driving field. The influence of the classical field and the purity of the initial state on the entanglement sudden death is
also studied. It is shown that the time of entanglement sudden death can be controlled by the classical driving fields. Particularly,
the entanglement sudden death phenomenon will disappear if the classical driving fields are strong enough. 相似文献