共查询到20条相似文献,搜索用时 15 毫秒
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通过解析和数值计算的方法研究了横场中具有周期性各向异性的一维XY自旋模型的量子相变和量子纠缠.主要讨论了周期为二的情况,即各向异性参数交替地取比值为α的两个值.结果表明,与横场中均匀XY模型相比,α=-1所对应的模型在参数空间的相图存在着明显的不同.原来的Ising相变仍然存在,没有了沿x和y方向的各向异性铁磁(FM_x,FM_y)相,即各向异性相变消失,出现了一个新的相,并且该相内沿x和y方向的长程关联函数相等且大于零,我们称新相为各向同性铁磁(FM_(xx))相.这是由于系统新的对称性所导致的.解析结果还说明系统在FM_(xx)相中的单粒子能谱有两个零点,是一个无能隙的相.最后,利用冯·诺依曼熵数值地研究了系统在新相内各点的量子纠缠,发现该相内每一点的冯·诺依曼熵的标度行为与均匀XY模型在各向异性相变处的相似,即S_L~1/3㏒_2L+Const. 相似文献
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Quantum Ising models in a transverse field are related to continuous-time percolation processes whose oriented percolation versions are contact processes. We study such models in the presence of quasiperiodic disorder and prove localization in the ground state, no percolation, and extinction, respectively, for sufficiently large disorder. 相似文献
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In this paper, we have studied the field and atomic dipole squeezing in the two-photon Jaynes-Cummings model when it is restricted to the following initial condition: the field in the thermal state and the atom in a coherent state. The relationship between the field and atomic dipole squeezing has also been discussed in detail. 相似文献
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We study quantum communication through an anisotropic Heisenberg XY chain in a transverse magnetic field. We find that for some time t and anisotropy parameter γ, one can transfer a state with a relatively high fidelity. In the strong-field regime, the anisotropy does not significantly affect the fidelity while in the weak-field regime the affect is quite pronounced. The most interesting case is the intermediate regime where the oscillation of the fidelity with time is low and the high-fidelity peaks are relatively broad. This would, in principle, allow for quantum communication in realistic circumstances. Moreover, we calculate the purity, or tangle, as a measure of the entanglement between one spin and all the other spins in the chain and find that the stronger the anisotropy and exchange interaction, the more entanglement will be generated for a given time. 相似文献
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We consider the statistical mechanics of a fluctuating string (1D solid-on-solid model) ofN columns with a contact energy term displaying a critical wetting transition. For this model we derive a contour integral representation for the finite-size partition function. From this representation we derive a polynomial representation and obtain the Lee-Yang zeros forN , 100. Through the asymptotic evaluation of the contour integral we evaluate the zeros for higherN. This asymptotic evaluation displays a Stokes phenomenon providing a different viewpoint of the mechanism by which a phase transition can arise, supplementing the picture of Lee and Yang. We also reproduce and extend somewhat the results of Smith for the finite-size scaling limit of the partition function. 相似文献
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The phase diagram of weakly coupled XXZ chains in a transverse magnetic field is studied using the mean-field approximation for the interchain coupling and known exact results for an effective one-dimensional model. The results are applied to the quasi-one-dimensional antiferromagnet Cs2CoCl4, and the value of interchain interaction in this compound is estimated. 相似文献
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We investigate the interplay of classical degeneracy and quantum dynamics in a range of periodic frustrated transverse field Ising systems at zero temperature. We find that such dynamics can lead to unusual ordered phases and phase transitions or to a quantum spin liquid (cooperative paramagnetic) phase as in the triangular and kagome lattice antiferromagnets, respectively. For the latter, we further predict passage to a bond-ordered phase followed by a critical phase as the field is tilted. These systems also provide exact realizations of quantum dimer models introduced in studies of high temperature superconductivity. 相似文献
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Fisher DS 《Physical review letters》1992,69(3):534-537
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D. V. Dmitriev V. Ya. Krivnov A. A. Ovchinnikov A. Langari 《Journal of Experimental and Theoretical Physics》2002,95(3):538-549
The one-dimensional spin-1/2 XXZ model in a transverse magnetic field is studied. It is shown that the field induces a gap in the spectrum of the model with the easy-plane anisotropy. Using conformal invariance, the field dependence of the gap is found at small fields. The ground state phase diagram is obtained. It contains four phases with the long-range order of different types and a disordered phase. These phases are separated by critical lines, where the gap and the long-range order vanish. Using scaling estimates, the mean-field approach, and numerical calculations in the vicinity of all critical lines, we find the critical exponents of the gap and the long-range order. It is shown that the transition line between the ordered and disordered phases belongs to the universality class of the transverse Ising model. 相似文献
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We study numerically the linear properties of periodic and quasiperiodic anisotropic layered media. Each anisotropic slab
can have arbitrary orientation of optic axis. We apply the general numerical code to recover the known results for solc filters.
We propose novel periodic structures where the location and width of the gaps can be controlled easily. We also study the
transmission properties of a Fibonacci sequence of anisotropic layers and show the interesting features like self-similarity
and scaling. 相似文献
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S. Thiem M. Schreiber 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(3):339-345
The light propagation through a stack of two media with different refractive indices, which are aligned according to different
quasiperiodic sequences determined by metallic means, is studied using the transfer matrix method. The focus lies on the investigation
of the influence of the underlying quasiperiodic sequence as well as the dependence of the transmission on the frequency,
the incidence angle of the light wave and different ratios of the refractive indices. In contrast to a periodically aligned
stack we find complete transmission for the quasiperiodic systems for a wide range of different refractive indices for small
incidence angles. Additional bands of moderate transmission occur for frequencies in the range of the photonic band gaps of
the periodic system. Further, for fixed indices of refraction we find a range of almost perfect transmission for angles close
to the angle of total reflection, which is caused by the bending of photonic transmission bands towards higher frequencies
for increasing incidence angles. Comparing with the results of a periodic stack the quasiperiodicity seems to have only an
influence in the region around the midgap frequency of a periodic stack. 相似文献
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This paper studies quantum diffusion in semi-infinite one-dimensional periodic lattice and quasiperiodic Fibonacci lattice. It finds that the quantum diffusion in the semi-infinite periodic lattice shows the same properties as that for the infinite periodic lattice. Different behaviour is found for the semi-infinite Fibonacci lattice. In this case, there are still C(t) - t^-δ and d(t) - t^β. However, it finds that 0 〈δ 〈 1 for smaller time, and δ = 0 for larger time due to the influence of surface localized states. Moreover, β for the semi-infinite Fibonacci lattice is much smaller than that for the infinite Fibonacci lattice. Effects of disorder on the quantum diffusion are also discussed. 相似文献
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L. S. Yakupova 《Russian Physics Journal》1993,36(7):698-702
The propagation is analyzed of a circularly polarized ultrashort videopulse of a transverse wave field in a spin system with an anisotropic spin-spin interaction. Several physical realizations of the given model are proposed. Soliton-like solutions are obtained without approximating the rotating wave and slowly varying envelopes. It is shown that the formation of a connected state of a two-component videopulse is possible for propagation velocities falling in a specific interval of values.Pacific Ocean Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 114–119, July, 1993. 相似文献
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The effects of the Dzyaloshinskii-Moriya interaction on the ground-state properties of the XY chain in a transverse field
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The effects of the Dzyaloshinski-Moriya (DM) interaction on the ground-state properties of the anisotropic XY chain in a transverse field have been studied by means of correlation functions and entanglement. Different from the case without the DM interaction, the excitation spectra εk of this model are not symmetrical in the momentum space and are not always positive. As a result, besides the ferromagnetic (FM) and the paramagnetic (PM) phases, a gapless chiral phase is induced. In the chiral phase, the von Neumann entropy is proportional to log2L (L is the length of a subchain) with the coefficient A ≈ 1/3, which is the same as that of the XY chain in a transverse field without the DM interaction for γ = 0 and 0 h ≤ 1. And in the vicinity of the critical point between the chiral phase and the FM (or PM) phase, the behaviors of the nearest-neighbor concurrence and its derivative are like those for the anisotropy transition. 相似文献