对量子力学中角动量的一点认识

指出了角动量算符Ｊ不存在本征值和本征矢量完全集,角动量算符Ｊ不描写一个可观察量以及角动量Ｊ不宜作为整体来讨论。     

Environmental recording of the angular momentum in quantum mechanics

We discuss the coupling of a quantum system through the angular momentum to the reservoir of quantum harmonic oscillators. In classical mechanics an observation of the oscillator trajectories allows one to determine the system's angular momentum. We discuss the quantum dynamics of the model. We show that the model of an observation of environmental coordinates can be related to some models of angular momentum measurement based on a stochastic Schrödinger equation.     

Equivalent angular momentum operators for second quantised operators

Formula useful for replacing second quantised operators by angular momentum operators are derived and commented on in the light of recent results on exchange interactions.     

通用的角动量阶梯算符

利用最新发展的非线性代数理论,给出了一般角动量阶梯算符所应满足的代数方程,并具体构造出了这些算符,所构造的北算符能对所有角动量本征态的解量子数和磁量子数起升降作用,具有很好的通用性。     

Canonical conjugate momentum of discrete label operators in quantum mechanics II: formalism

The formalism developed in Part I of the present paper for the conjugate momentum of label operators is applied to standard physical examples, such as the regular one-dimensional lattice, the one-dimensional box, and the angular momentum of the plane rotator. A non-standard application is also considered, i.e., the timeoperator, conjugate to the one-dimensional harmonic Hamiltonian.     

Canonical conjugate momentum of discrete label operators in quantum mechanics I: formalism

We discuss the inadequacy of the standard definition of canonical conjugation for a quantum operator having adiscrete spectrum. A different definition is proposed, based on the analogy betweencontinuous anddiscrete translations (or rotations). This definition can be applied to special operators which we calllabel operators. The general form of the conjugate momentum of a label operator is found and the resulting canonical commutation rules are discussed. It is shown that the canonical commutator acts like ac number in itsdomain _I , but the domain does not coincide with the whole Hilbert space. The properties of the subspace _I are also discussed.     

Traces of products of angular momentum operators

Traces of products of angular momentum operators in a spherical or cartesian basis are common in the theory of atomic levels in fields, in the theory of nuclear orientation and of asymmetric top moments. Conventional angular momentum techniques lead to difficult and cumbersome calculations. In the present paper Schwinger's coupled boson representation is used in straightforward calculations of angular momentum and spherical tensor traces, of matrix elements and of asymmetric top moments. Only simple algebra, elementary multiplication and summation of integers are necessary. The method considerably simplifies calculations with angular momentum operators.     

Unitary transformations with spin angular momentum operators

Useful formulae for replacing an exponentiated spin scalar product by a finite sum of powers of this product, are presented in the context of Coulomb interactions between magnetic ions and conduction electrons in metals.     

Quantum mechanics in discrete space and angular momentum

Recently we have studied quantum mechanics of bounded operators with a discrete spectrum. In particular, we derived an expression for the commutator[Q, P] of two bounded operators whose spectrum is discrete, and we showed that in the limit of a continuous spectrum the commutator becomes the standard one of Heisenberg. In this paper we show that the angular momentum operator and the phase operator satisfy the new commutation relation. We also briefly discuss the problem of the canonical phase operator conjugate to the number operator.     

Minimum uncertainty states for angular momentum operators

Minimum uncertainty states for an angular momentum system are presented and some of their properties discussed.     

轨道角动量分量算符的本征函数间的变换

本文讨论了不同轨道角动量分量算符本征函数间的变换关系,给出了对应的变换系数的计算方法,求解了几个比较常见情形l=1,2,3的变换系数,得到了各个变换系数之间的规律.     

Tensor operators in noncommutative quantum mechanics

Some consequences of promoting the object of noncommutativity theta(ij) to an operator in Hilbert space are explored. Its canonical conjugate momentum is also introduced. Consequently, a consistent algebra involving the enlarged set of canonical operators is obtained, which permits us to construct theories that are dynamically invariant under the action of the rotation group. In this framework it is also possible to give dynamics to the noncommutativity operator sector, resulting in new features.     

Antiunitary symmetry operators in quantum mechanics

A criterion to decide that some symmetries of a quantum system must be realized as antiunitary operators is given. It is based on some mathematical theorems about the second cohomology group of the symmetry group when expressed in terms of those of a normal subgroup and the corresponding factor group. It is also shown that this criterion implies that the only possibility for the unitary subgroup in the Galilean case is that generated by the space reflection and the connected component containing the identity; otherwise only massless systems would arise.     

SU(3) symmetry for orbital angular momentum and method of extremal projection operators

Basic elements of the formalism of the theory that is based on the representations of the SU(3) group for the case of its reduction to the SO(3) subgroup of orbital angular momentum and which is widely used in theoretical physics is presented in a systematic and consistent form. Irreducible SU(3) ? SO(3) bases, both a nonorthogonal one chosen among Elliott vectors and an orthogonal one obtained from a nonorthogonal one by diagonalizing the Bargmann-Moshinsky operator, are described in detail. In particular, it is shown that there is wide arbitrariness in choosing a basis among Elliott vectors. The SU(3) ? SO(3) Clebsch-Gordan coefficients are considered in detail, along with all of their classical symmetry properties. A brief survey (history of discovery) of the method of extremal projection operators for Lie symmetries (Lie algebras and superalgebras and their quantum analogs) is given.     

角动量量子数l的升降算符和球谐函数的生成

1999年喀兴林先生在<高等量子力学>一书中首次提出角动量量子数l的升降算符,这个算符其实是一秩不可约张量算符的一个简单实现.当给定一个磁量子数m,降算符能给出最小量子数l的状态,进而得到全部球谐函数的最低态|0,0>.而通过升降算符的恰当组合,作用在这个最低态上就可以生成任意球谐函数|lm>.     

Special topics in the quantum theory of angular momentum

Two special topics in the quantum theory of angular momentum are discussed in this article. They are: (i) the relationship between the coupling and recoupling coefficients (for two and three angular momenta, respectively) and sets of generalized hyper-geometric functions of unit argument; and (ii) the ‘non-trivial’ or polynomial zeros of angular momentum coefficients and their classification.