A general approach to the description of an angle and phase is given on the basis of the
kq representation. It is shown that an angular coordinate in quantum mechanics has to be treated as a quasicoordinate in order to avoid inconsistencies. The
kq representation leads to a consistent definition of the angular-momentum-angle degree of freedom. Using the correspondence between classical and quantum mechanics for the phase of a harmonic oscillator, operators are defined that form a new quantum-mechanical representation. This representation clarifies the concept of the phase and sheds light on the general understanding of rotations in quantum mechanics.
Contrary to the usual view that quantum mechanics in configuration space has, in general, only one algebaic representation( the Heisenberg algebraic representation), we have proved that quantum mechanics in configuration space has, in general, alternative algebraic representations: (i) In a finite domain of configuration space, it can be expressed in terms of su(2) algebra; (ii) in an infinite domain of configuration space, it can be expressed in terms of su(l,l) algebra.The above results open a new possibility to reformulate quantum mechanics and provide more mathematical tools to solve diverse physical problems.Nonlinear relations of different Lie algebas may imply a unification of Lie algebras and their physical implications ( the quantum motion modes ) in a deeper nonlinear domain.This observation raises challenging mathematical and physical questions.