Decision theory and information propagation in quantum physics

In recent papers, Zurek [(2005). Probabilities from entanglement, Born's rule p_k=|ψ_k|² from entanglement. Physical Review A, 71, 052105] has objected to the decision-theoretic approach of Deutsch [(1999) Quantum theory of probability and decisions. Proceedings of the Royal Society of London A, 455, 3129–3137] and Wallace [(2003). Everettian rationality: defending Deutsch's approach to probability in the Everett interpretation. Studies in History and Philosophy of Modern Physics, 34, 415–438] to deriving the Born rule for quantum probabilities on the grounds that it courts circularity. Deutsch and Wallace assume that the many worlds theory is true and that decoherence gives rise to a preferred basis. However, decoherence arguments use the reduced density matrix, which relies upon the partial trace and hence upon the Born rule for its validity. Using the Heisenberg picture and quantum Darwinism—the notion that classical information is quantum information that can proliferate in the environment pioneered in Ollivier et al. [(2004). Objective properties from subjective quantum states: Environment as a witness. Physical Review Letters, 93, 220401 and (2005). Environment as a witness: Selective proliferation of information and emergence of objectivity in a quantum universe. Physical Review A, 72, 042113]—I show that measurement interactions between two systems only create correlations between a specific set of commuting observables of system 1 and a specific set of commuting observables of system 2. This argument picks out a unique basis in which information flows in the correlations between those sets of commuting observables. I then derive the Born rule for both pure and mixed states and answer some other criticisms of the decision theoretic approach to quantum probability.     

有机铁磁体的研究进展及应用前景

阐述了有机铁磁体的研究动态。根据铁磁理论制造有机铁磁体的主要途径有有机金属复合物铁磁体与纯有机铁磁体,本文对这两种有机铁磁体特别是对纯有机铁磁体在目前所取得的研究成果做了较为详细的介绍与讨论,根据有机铁磁体的特性对有机铁磁体的应用前景进行了展望。     

海森堡反铁磁模型的代数结构和能量本征值

XYZ海森堡反铁磁模型的哈密顿量在自旋波近似下具有su(1,2)李代数结构,利用代数对角化方法,通过相似变换得到该模型的能量本征值,为理论分析该模型在物理中的性质和代数对角化方法的应用提供了更广泛的依据.     

交换积分变化对低温二维亚铁磁体能谱的影响

运用Heisenberg交换作用模型、spin-wave和Green＇s function方法研究了与低维有机磁性系统接近的二维正方晶格绝缘亚铁磁体的自旋波谱,并分析了不同方向上能谱谱线随系数J1/J2增加的变化规律,得到了如下结论：随磁性离子间的交换积分发生改变,磁振子能谱也发生了改变,沿某一方向能谱的变化与此方向上交换积分的变化密切相关。系统沿某一方向上交换积分的变化,导致形成所谓“自旋梯”时,谱线退化成5条能级,除最大的磁振子能谱线与最小的磁振子能谱线外,其余3条磁振子能谱线是二重简并的．系统的磁振子能谱E1、E3、E5、E7、与E6、E8、E2、E4关于E／J=0线对称分布。     

零温时二维绝缘铁磁体的磁振子寿命

在二维正方绝缘铁磁系统基础上建立了一个磁振子-声子相互作用模型.利用格林函数方法研究了磁振子-声子相互作用下的二维绝缘铁磁体的磁振子衰减,计算了布里渊区的主要对称点线上的-ImΣ*(1)(k).发现在布里渊区边界区域磁振子衰减很明显,但小波矢区(kxa/π<0.22附近)磁振子衰减非常弱.零温时磁振子衰减有极大值.比较了纵向声子与横向声子对磁振子衰减的影响,也讨论了各项参数的变化对磁振子衰减的影响.根据关系式-ImΣ*(1)(k)=/(2τ)可以对磁振子寿命进行判断.     

尖晶石型LiMn2O4的磁性研究

利用化学方法制备了尖晶石结构的LiMn2O4材料,并对其进行了磁性测量．结果表明：随着Li／Mn比例的增加。Mn^＋4数量增加,90°的Mn^＋4-O-Mn^＋4的铁磁相互作用使居里温度升高,样品由反铁磁性逐渐向铁磁性过渡．     

非均匀磁场作用下四量子比特海森堡自旋链中的热纠缠

研究在外加非均匀磁场作用下的四量子比特海森堡XX模型中的纠缠特性,并得到具有周期性边界条件系统中纠缠度量的解析表达.发现能得到较高的成对纠缠,这意味着系统中的磁不均匀性可以提高某些量子比特对的热纠缠度.     

自旋轨道耦合对铁磁/半导体/绝缘体多层膜结构中隧穿性质的影响

利用传递矩阵方法,计算了自旋轨道耦合对铁磁/半导体/绝缘体多层膜结构中隧穿性质的影响.结果表明,当半导体和铁磁体之间是绝缘接触时,体系的输运性质发生明显改变,同时出现了自旋反转效应.     

海森伯格XXZ模型的热纠缠

负值度(Negativity)是一种通用的纠缠度量,可方便地计算两体量子系统的纠缠度.利用负值度研究了两量子比特各向异性海森伯格XXZ模型的热纠缠,讨论了在热平衡时温度和外加磁场对热纠缠的影响.当温度小于临界温度时,热纠缠的大小依赖于外加磁场的强弱;当温度大于临界温度时,纠缠消失.     

(d+1)维Heisenberg超薄膜的解析研究

采用变分累积展开法研究了超立方格点上任意自旋的量子ｈｅｉｓｅｎｂｅｒｇ薄膜的临界点。从自由能的解析性质出发,原则上能计算作为多层膜层数ｌ函数的临界约化温度θ＾（ｎ）（ｌ）到任意累积展开级次ｎ。给出了θ＾（ｎ）（ｌ）的前三级解析表达式和数值结果,并对结果作了分析和讨论。