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1.
通过分析系统的杂质位与其余部分间的纠缠N1-A以及单个正常位与其余部分间的纠缠NL-A研究了匀强磁场作用下含杂质Heisenberg XX链的纠缠特性.研究表明三量子位时纠缠存在的临界温度依赖于杂质参数J1和匀强磁场B.研究发现,当量子位L为奇数时,纠缠N1-A随量子位的增加而增大,而L为偶数时则相反,并且量子位L为偶数时的纠缠大于量子位L为奇数时的纠缠;对NL-A, 量子位L为奇数时,纠缠随杂质参数J1的变化与L=3类似,而L为偶数时纠缠随杂质参数|J1|的增加而增加. 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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CRITICAL CURRENT DENSITY AND FLUX PINNING CHARACTERISTICS IN MELT-TEXTURED Y0.6Er0.4Ba2Cu3Oy SUPERCONDUCTOR
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We prepared highly textured YBa2CuOy and Y0.6Er0.4Ba2Cu3Oy bulk samples by a powder melting process method under the same conditions and studied the magnetic properties and flux pinning character istics. It is found that the Jc estimated by the Bean's model decreases with the magnetic field according to a power law Jc∝B-n (n<0.55), suggesting that Jc values of these materials are controlled by the flux pinning rather than weak links. Also, Jc and flux pinning are improved by the Er addition. The reduction of the size of Y2BaCuO5 particles, magnetic pinning and stress-field pinning caused by the Er addition may be responsible for the enhancement of Jc and flux pinning. 相似文献
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The Doppler-limited absorption spectra of 14N and 15N atoms were measured around 800 nm using concentration modulation spectroscopy to study their isotope shifts. The nitrogen atoms were generated by discharging molecular nitrogen buffered with helium in a homemade discharge tube. The isotope shifts of four multiplets (3s4PJ→3p4DJo, 3s4PJ→3p4PJo, 3s2DJ→5s2PJo, and 3p2PJo→5s2DJo) were measured and their J-dependent specific mass shifts were observed and discussed. 相似文献
7.
Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, I
c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed
that while the control side showed a J
c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J
c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of
J
c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection
length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length
has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection. 相似文献
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首先把本征值方程投影到导带的子空间中, 进而得到AlGaN/GaN量子阱中第一、二子带的Rashba自旋劈裂系数(α 1, α 2)和子带间自旋-轨道耦合系数η12. 然后自恰求解薛定谔方程和泊松方程计算了不同栅压的量子阱中的α 1, α 2和η12, 并分别讨论了量子阱阱层、左右异质结界面和垒层对它们的贡献. 结果表明可以通过栅压来调节自旋-轨道耦合系数, 子带间自旋轨道耦合系数η12比Rashba自旋劈裂系数α 1, α 2小, 但基本在同一数量级. 相似文献
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颗粒物质是一种复杂的能量耗散体系. 颗粒间的摩擦和黏滞作用可使冲击荷载引起的能量有效衰减, 颗粒间的力链结构又可将瞬时局部冲击荷载进行空间扩展和时间延长, 达到良好的缓冲效果. 为研究颗粒物质对冲击荷载的缓冲性能, 本文采用重力作用下球体冲击筒内颗粒物质的试验系统, 研究了筒体底部作用力在颗粒材料、颗粒厚度等因素影响下的变化规律. 试验结果表明: 非规则颗粒具有更加良好的缓冲性能, 粗颗粒的缓冲性能略高于细颗粒. 颗粒厚度H是影响缓冲性能的重要因素, 并存在一个临界厚度Hc. 当H<Hc时, 缓冲性能随H的增加而增强; 当H>Hc时, H对缓冲效果的影响不再显著. 以上研究是在同一冲击能量下进行的, 而对于不同冲击能量下的Hc还需要深入开展. 通过颗粒物质对冲击荷载缓冲性能的试验研究, 可揭示颗粒材料的基本物理力学行为, 为其在缓冲减振领域中的应用提供依据. 相似文献
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We study the time evolution of entanglement of two spins in an anisotropically coupled quantum dot interacting with the unpolarised nuclear spins environment. We assume that the exchange coupling strength in the z direction J z is different from the lateral one J l . We observe that the entanglement decays as a result of the coupling to the nuclear environment and reaches a saturation value, which depends on the value of the exchange interaction difference J = ‖J l ? J z ‖ between the two spins and the strength of the applied external magnetic field. We find that the entanglement exhibits a critical behaviour controlled by the competition between the exchange interaction J and the external magnetic field. The entanglement shows a quasi-symmetric behaviour above and below a critical value of the exchange interaction. It becomes more symmetric as the external magnetic field increases. The entanglement reaches a large saturation value, close to unity, when the exchange interaction is far above or below its critical value and a small one as it closely approaches the critical value. Furthermore, we find that the decay rate profile of entanglement is linear when the exchange interaction is much higher or lower than the critical value but converts to a power law and finally to a Gaussian as the critical value is approached from both directions. The dynamics of entanglement is found to be independent of the exchange interaction for an isotropically coupled quantum dot. 相似文献
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An entangled quantum refrigerator working with a three-qubit one-dimensional isotropic Heisenberg XX model in a constant external magnetic field is constructed in this paper. Based on the quantum first law of thermodynamics, the expressions for several basic thermodynamic quantities such as the heat transferred, the net work and the coefficient of performance are derived. Moreover, the influence of the thermal entanglement on the basic thermodynamic
quantities is investigated. Several interesting features of the variation of the basic thermodynamic quantities with the thermal entanglement in zero and nonzero magnetic field are obtained. 相似文献
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A thermal entangled quantum refrigerator based on a two-qubit Heisenberg model with Dzyaloshinskii-Moriya interaction in an external magnetic field
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Based on an isotropic two spin-1/2 qubits Heisenberg model with the Dzyaloshinskii-Moriya interaction in an external magnetic field, we have constructed an entangled quantum refrigerator. Expressions for the basic thermodynamic quantities, i.e., the heat exchanged, the net work input, and the coefficient of performance, are derived. Some intriguing features and their qualitative explanations in zero and non zero magnetic fields are given. The influence of the thermal entanglement on the refrigerator is investigated. The results obtained here have general significance and will be helpful to understand the performance of an entangled quantum refrigerator. 相似文献
14.
以带有Dzyaloshinski-Mariya 相互作用的两比特XXZ模型为工作物质构建纠缠量子热机. 在量子热力学平衡态下, 采用Kieu的形式描述了做功与热传递.对于不同的各向异性参数, 分析了热机循环中量子纠缠与热传递、做功以及机械效率等热力学量之间的关系. 结果表明: 在这个纠缠体系中, 热力学第二定律依然成立; 机械效率的等值线图是环状曲线; 当各向异性参数Δ较小时, 热机在C1 > C2 和C1 < C2 两区域运行, 当增大Δ值时, 热机只在C1 > C2 区域运行.
关键词:
量子热机
并发度
机械效率 相似文献
15.
给出了依赖强度耦合双模多光子过程Jaynes-Cummings模型的有效哈密顿量.在强场条件下,分别用量子约化熵和量子相对熵研究了上述模型中原子与场之间的纠缠以及双模相干场的模间纠缠演化.研究表明,这两类纠缠演化均与原子跃迁时吸收(或发射)的光子数k密切相关.同时,还揭示了双光子过程(k=1)和多光子过程(k≥2)中不同的纠缠特性.讨论了纠缠态的制备,制备了与时间无关的原子-场的Einstein-Podolsky-Rosen态和双模相干场的模间纠缠态. 相似文献
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We investigated the quantum entanglement in spin-1 Heisenberg XY chain for two-spin-qutrit and multi-particle systems. As a measure of the entanglement, the negativity of this state was
analyzed as a function of the temperature and the magnetic field. We gave some numerical results and discussed them in detail.
We found that the negativity increases monotonously with the coupling constants |J
1| and |J
2|, and it showed a symmetry with respect to the point of J
1 = 0 and J
2 = 0. In addition to the above features, there is evidence that the critical temperature is independent of the length of the
chain. 相似文献
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We present an efficient entanglement purification protocol (EPP) with controlled-not (CNOT) gates and linear optics. With the CNOT gates, our EPP can reach a higher fidelity than the conventional one. Moreover, it does not require the fidelity of the initial mixed state to satisfy F>1/2. If the initial state is not entangled, it still can be purified. With the linear optics, this protocol can get pure maximally entangled pairs with some probabilities. Meanwhile, it can be used to purify the entanglement between the atomic ensembles in distant locations. This protocol may be useful in long-distance quantum communication. 相似文献
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We investigate the entanglement of the three-qubit Heisenberg XXX chain in the presence of impurity and obtain the analytical expressions of the concurrence C. It is found that for impurity entanglement, C appears only when J
1 > J for J > 0, and J
1 > 0 for J < 0, and in these two regions C increases with the increase of J
1, so is the critical temperature T
c. When J
1 ≫ | J |, C reaches its maximum value 0.5 and T
c reaches the asymptotic value T
c = 3.41448J
1. For entanglement between the normal lattices, C appears only when J > 0 and −2J < J
1 < J, and initially increases with the increase of J
1 and arrives at the maximum value C
max = (e4J/T
−3)/(e4J/T
+ 3) before it decays to zero gradually, so is the critical temperature T
c with, however, the maximum value T
cmax = 4J/In3.
Supported by the Natural Science Research Project of Shaanxi Province (Grant No. 2004A15) 相似文献
20.
Quantum entanglement and quantum nonlocality of N-photon entangled states |\psiN m\rangle
=Cm[\cos\gamma|N-m\rangle1|m\rangle2 +\e{\i\θm}\sin\gamma|m\rangle1|N-m\rangle2] and their superpositions are studied. We point out that the relative
phase θm affects the quantum nonlocality but not the quantum
entanglement for the state |\psiN m\rangle. We show that
quantum nonlocality can be controlled and manipulated by adjusting
the state parameters of |\psiN m\rangle, superposition
coefficients, and the azimuthal angles of the Bell operator. We
also show that the violation of the Bell inequality can reach its
maximal value under certain conditions. It is found that quantum
superpositions based on |\psiN m\rangle can increase the
amount of entanglement, and give more ways to reach the maximal
violation of the Bell inequality. 相似文献