Model-independent constraints on spin observables

We discuss model-independent constraints on spin observables in exclusive and inclusive reactions, with special attention to the case of photoproduction.     

Unsharp spin observables, non-locality and Fry, Walther and Li experiment

Recently it has been demonstrated that Bell inequalities for spin 1/2 particles must be modified if unsharp spin observables are considered, and furthermore, the modified Bell inequalities may not be violated by quantum mechanics if the observables are sufficiently unsharp. In case of massive particles there may be more imperfection than seems to appear in the photon EPR experiments. So the experiment proposed by Fry, Walther and Li can place experimental limits on the unsharpness of spin variables. It sheds new light on the much debated issues like non-local correlations in quantum mechanics.     

Positivity constraints on initial spin observables in inclusive reactions

For any inclusive reaction of the type A1(spin 1/2)+A2(spin 1/2)-->B+X, we derive new positivity constraints on spin observables and study their implications for theoretical models in view, in particular, of accounting for future data from the polarized pp collider at Brookhaven RHIC. We find that the single transverse spin asymmetry A(N), in the central region for several processes, for example, jet production, direct photon production, and lepton-pair production, is expected to be such that |A(N)| < or approximately 1/2, rather than the usual bound |A(N)|< or =1.     

Berry's phase,density matrices and incompatible observables

Adiabatically time-varying parameter-dependent cyclic Hamiltonians are known to generate Berry's phase in state vectors in addition to the usual dynamical phase. Using the standard algorithm for collapse into a mixture following a quantum measurement process, we investigate the general nature of measurements in which the effects of Berry's phase, introduced at some intermediate stage of the measurement process, persist in the final collapsed density matrix. We find that it is possible to construct a sequence of a preparation followed by a measurement of an observable incompatible with the prepared state, where the collapsed density operator carries intermediate changes of phase in pure states; hence unitary time evolution alone is not essential for the observation of geometrical phases. This result confirms similar suggestions made by other investigators.     

A value rule for non-maximal observables

A value rule for contextualized non-maximal observables, the non-maximal value rule (NMVR), is proven from the value rule for maximal observables (VR) and the statistical functional composition principle (STAT FUNC). A consequence of NMVR, the non-maximal eigenvalue rule (NMER), is then applied to a reformulation of Mermin's Bell-EPR non-locality proof, putting this proof in the same form as other algebraic non-locality proofs. Two such reformulations have been given previously. NMVR implies an important technical lemma, which is assumed in these two reformulations, thus giving this one the same degree of rigour as other proofs, despite its greater simpliticity.     

Model-independent analysis of the neutral-current interaction in the inclusive neutrino reactions

On the basis of some general assumptions on the deep inelastic structure functions, such as scaling and chiral symmetry we determine the values of {(H _V ³)²+(H _A ³)²}+η{(H _V ⁰)²+(H _A ⁰)²} andH _V ³ H _A ³+ηH _V ⁰ H _A ⁰ whereH _V ^3,0 andH _A ^3,0 are the four coupling constants characterizing the hadronic neutral current andη is the ratio of the isoscalar to isovector structure functions. General expressions are given for the kinematical averages 〈v〉 and 〈Q ²〉 for the neutral-current reactions in terms of the coupling constants. This analysis does not depend on the validity of the quark-parton model.     

Conservation of channel spin in transfer reactions

The conservation of channel spin implying that the spin of the initial bound pair coupled to that of the initial free particle should result in the same channel spin as the spin of the final bound pair coupled to the spin of the final free particle, follows as a consequence of three-body theory of transfer reactions with the assumption of separability of two-bodyt-matrix. To test the validity of this principle we look at the experimental data on stripping reactions on even-even nuclei. We find that although reactions to channels not conforming to channel spin conservation are not altogether ruled out, the cross-sections of reactions violating channel spin conservation are much smaller than those conforming to channel spin conservation.     

Natural geometric representation for electron local observables

An existence of the quartic identities for the electron local observables that define orthogonality relations for the 3D quantities quadratic in the electron observables is found. It is shown that the joint solution of the quartic and bilinear identities for the electron observables defines a unique natural representation of the observables. In the natural representation the vector type electron local observables have well-defined fixed positions with respect to a local 3D orthogonal reference frame. It is shown that the natural representation of the electron local observables can be defined in six different forms depending on a choice of the orthogonal unit vectors. The natural representation is used to determine the functional dependence of the electron wave functions on the local observables valid for any shape of the electron wave packet.     

Mean spin direction and spin squeezing in superpositions of spin coherent states

We consider the mean spin direction (MSD) of superpositions of two spin coherent states (SCS) | ± μ〉, and superpositions of | μ〉 and | μ*〉 with a relative phase. We find that the azimuthal angle exhibits a π transition for both states when we vary the relative phase. The spin squeezing of the states, and the bosonic counterpart of the mean spin direction are also discussed.      

Interaction between classical and quantum systems and the measurement of quantum observables

Quantum mechanics presumes classical measuring instruments with which they interact. The problem of measurement interaction between classical and quantum systems is posed and solved. The restriction to compatible measurements comes about naturally as the condition for the integrity of the classical system. A technical device is the perspective on classical mechanics as quantum mechanics with essentially hidden dynamical variables. Work supported in part by U.S. Atomic Energy Commission, ERDA.     

New observables in topological instantonic field theories

Instantonic theories are quantum field theories where all correlators are determined by integrals over the finite-dimensional space (space of generalized instantons). We consider novel geometrical observables in instantonic topological quantum mechanics that are strikingly different from standard evaluation observables. These observables allow jumps of special type for the trajectory (at the point of insertion of such observables). They do not (anti)commute with evaluation observables and raise the dimension of the space of allowed configurations, while the evaluation observables lower this dimension. We study these observables in geometric and operator formalisms. Simple examples are explicitly computed; they depend on the linking of points.     

一种输出自旋流的装置--自旋池

文章作者设计了一种能够给未来的自旋电路提供驱动自旋流的动力装置，即自旋池．该自旋池有如下四个基本特点：(1)有两个极能使自旋流从一个极流入，从另一个极流出，从而建立一个闭合的自旋回路；(2)有一个能量源；(3)能保持自旋相干；(4)能输出不附加任何净电荷流的纯自旋流，值得注意的是，该自旋池能通过现有的技术手段实现。     

Robust nuclear observables and constraints on random interactions

The predictions of the interacting boson model two-body random ensemble are compared to empirical results on nuclei from Z = 8-100. Heretofore unrecognized but robust empirical trends are identified and related both to the distribution of valence nucleon numbers and to the need for and applicability of specific, nonrandom interactions. Applications to expected trends in exotic nuclei are discussed.     

瞬态自旋光栅系统的建设及其在自旋输运研究中的应用

简要介绍了瞬态光栅系统原理及光路的建设,包括瞬态光栅的产生与探测.采用了外差探测法（heterodyne detection）,大大提高了信噪比.利用瞬态自旋光栅系统,研究了(110)方向生长的本征GaAs/AlGaAs单量子阱中自旋输运特性,测得室温下电子自旋的扩散常数D_s=551 cm/s. 关键词： 瞬态自旋光栅 自旋扩散 自旋输运 自旋弛豫     

从自旋冰到自旋液态的渡越——结构与磁性质的演化

使用固相反应法得到了Ho_2-xTb_xTi₂O₇（x=0,05,1,15,2）系列多晶样品.X射线衍射（XRD）实验与2K到300K温度区间的直流磁化率测量结果显示,随着Tb即是x的增加,体系由自旋冰Ho₂Ti₂O₇向自旋液Tb₂Ti₂O_{7关键词： 自旋冰 自旋液体 自旋阻挫 晶格结构}     

Temporal evolution of spin accumulation in nonlocal spin valves

A temporal evolution of spin signals has been observed in nanoscale Co/Cu nonlocal spin valves. The spin diffusion length of Cu increases from ∼300 to ∼350 nm measured at 295 K over a 50-day period in the ambient environment after the fabrication of the devices. This is attributed to a gradual oxidation in the regions near the side surfaces of the Cu channel, where Co impurities are implanted during the fabrication. An increase of spin injection polarization is also found and attributed to the change of oxidation states at the interfaces.