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广西师范大学学报:自然科学版

J=J1+J2时耦合与非耦合表象的变换通式

张振华, 彭景翠

Published Jan 1, 2000• 0 citations
OpenAlex

Abstract

针对矢耦系数采用Racah表达式进行计算过于复杂,而矢耦系数表又过于零碎的问题,提出了j=j1+j2时,耦合表象与非耦合表象的变换通式,并用数学归纳法予以严格证明,同时将单电子的表象变换作为特例,用此变换通式予以计算,与现有文献的结论完全相同。该变换通式简洁对称,易于使用。

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arXiv:cond-mat/0006448•Physical review. B, Condensed matter•Sep 1, 2000•26 citations
针对矢耦系数采用Racah表达式进行计算过于复杂,而矢耦系数表又过于零碎的问题,提出了j=j1+j2时,耦合表象与非耦合表象的变换通式,并用数学归纳法予以严格证明,同时将单电子的表象变换作为特例,用此变换通式予以计算,与现有文献的结论完全相同。该变换通式简洁对称,易于使用。
We study the J1-J1'-J2 quantum spin model on the two-dimensional square lattice using the coupled cluster method. We compare and contrast the influence of the interchain coupling J1' on the zero-temperature phase diagrams for the two spin values s = 1/2 and s = 1. Our most important result for the s = 1/2 case is the predicted existence of a quantum triple point (QTP) at (J1' ≈ 0.60 ± 0.03, J2 ≈ 0.33 ± 0.02) when J1 = 1. Below the QTP (J1'/J1 ≤ 0.60) we predict a second-order phase transition between the quasi-classical Neel and stripe-ordered phases, whereas the corresponding classical model, which contains only these two phases for all spin values s, yields a first-order transition. Above the QTP (J1'/J1 ≥ 0.60) an intermediate disordered phase emerges, which has no classical counterpart. By contrast, the situation for s = 1 is qualitatively different. Instead of a QTP where three phases co-exist, we now predict a quantum tricritical point at (J1' ≈ 0.66 ± 0.03, J2 ≈ 0.35 ± 0.02) when J1 = 1, where a line of second-order phase transitions between the quasi classical Neel and stripe-ordered phases (for J1'/J1 ≤ 0.66) meets a line of first-order phase transitions between the same two states (for J1'/J1 ≥ 0.66). Surprisingly, we find no evidence at all for any intermediate disordered phase in the s = 1 case.
Two entangled particles in threedimensional Hilbert space (per particle) are considered in an EPR-type arrangement. On each side the Kochen-Specker observables {J12,J22,J32}\{J_1^2,J_2^2,J_3^2\}{J12​,J22​,J32​} and {Jˉ12,Jˉ22,J32}\{\bar J_1^2, \bar J_2^2,J_3^2\}{Jˉ12​,Jˉ22​,J32​} with [J12,Jˉ12]≠0[J_1^2,\bar J_1^2]\neq 0[J12​,Jˉ12​]=0 are measured. The outcomes of measurements of J32J_3^2J32​ (via J12,J22J_1^2,J_2^2J12​,J22​) and J32J_3^2J32​ (via Jˉ12,Jˉ22\bar J_1^2,\bar J_2^2Jˉ12​,Jˉ22​) are compared. Although formally J32J_3^2J32​ is associated with the same projection operator, a strong form of quantum contextuality states that an outcome depends on the complete disposition of the measurement apparatus, in particular whether J12J_1^2J12​ or Jˉ12\bar J_1^2Jˉ12​ is measured alongside. It is argued that in this case it is impossible to measure contextuality directly, a necessary condition being a non-operational counterfactuality of the argument.
通过理论计算与量子计算模拟机模拟两种方法研究了波-粒量子行走的演化过程与性质。通过量子控制操作使量子行走中的行走者处于相对相位的波-粒相干叠加态。利用后选择操作实现了量子行走以相干和混合两种不同方式,从多路径相干的波的状态到无相干的粒子的状态的连续调控。由于量子的干涉性,相干和混合两种方式存在本质的区别,通过位置方差对两种方式的具体特征进行刻画。最后通过量子计算模拟机模拟了波-粒量子行走的演化过程。当行走者处于波-粒相干态时,通过一次测量能够同时观测到两个完全不同的性质。通过调节波-粒相干态的相对相位,可以实现对行走者扩散速率的控制。
The surface scaling behavior of classical isotropic Heisenberg magnets is investigated by Monte Carlo methods in d=3d=3d=3 dimensions for various values of the surface-to-bulk coupling ratio J1/J.{J}_{1}/J.J1​/J. For J1/J< 1.0,{J}_{1}/J<~1.0,J1​/J< 1.0, critical behavior according to the ordinary surface universality class is found. Estimates for magnetic surface exponents are presented and compared to older estimates and their theoretical counterparts. For J1/J> 2.0,{J}_{1}/J>~2.0,J1​/J> 2.0, scaling is still valid with effective exponents which depend on J1/J.{J}_{1}/J.J1​/J. The surface structure factor S1(p,L){S}_{1}(p,L)S1​(p,L) is investigated at bulk criticality as a function of the momentum transfer p parallel to the surface and the system size L. For J1/J< 1.0{J}_{1}/J<~1.0J1​/J< 1.0 and J1/J> 2.0{J}_{1}/J>~2.0J1​/J> 2.0 the full p dependence of S1(p,L){S}_{1}(p,L)S1​(p,L) can be captured by generalized shape functions to a remarkable accuracy. Profiles of the magnetization and the energy density also confirm scaling, where for J1/J< 1.0{J}_{1}/J<~1.0J1​/J< 1.0 the ordinary surface universality class is recovered and for J1/J> 2.0,{J}_{1}/J>~2.0,J1​/J> 2.0, scaling with J1/J{J}_{1}/JJ1​/J dependent exponents is found. For J1/J=1.5{J}_{1}/J=1.5J1​/J=1.5 the system displays a striking crossover behavior from spurious long-range surface order to the ordinary surface universality class. For J1/J> 2.0{J}_{1}/J>~2.0J1​/J> 2.0 the effective scaling laws must be interpreted as nonasymptotic and the value J1/J=1.5{J}_{1}/J=1.5J1​/J=1.5 marks a crossover regime, in which the crossover from the nonasymptotic to the asymptotic (ordinary) surface scaling behavior can be resolved within numerically attainable system sizes.