ADIABATIC MOTION OF A QUANTUM PARTICLE IN A 2-DIMENSIONAL MAGNETIC-FIELD

The adiabatic motion of a charged, spinning, quantum particle in a two -dimensional (i.e. of constant direction) magnetic field is studied. A suitable set of operators generalizing the kinematical momenta and th e guiding centre operators of a particle moving in a homogeneous magne tic field is constructed. This allows us to separate the two degrees o f freedom of the system into a fast and a slow one which are, in the c lassical limit, the rapid rotation of the particle around the guiding centre and the slow guiding centre drift. In terms of these operators the Hamiltonian of the system can be rewritten as a power series in th e magnetic length l(B) = root HBARc/eB, and the fast and slow dynamics separates. The effective guiding centre Hamiltonian is obtained to se cond order in the adiabatic parameter l(B) and reproduces correctly th e classical limit.