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For a charged particle (charge , mass ) in a magnetic field, the canonical form for the nonrelativistic Hamiltonian is given by

,

where is the vector potential. The magnetic field is given by . We consider an electron () confined to the - plane, bound by an isotropic harmonic-oscillator potential and subjected to a constant magnetic field in the direction. This field can be represented by the vector potential , such that

,

,

.

The Schrödinger equation, in Cartesian coordinates, can then be written

.

Expanding the squares, we obtain

.

Note now that , the component of angular momentum, and that , the Larmor frequency for an electron. It is convenient now to transform to cylindrical coordinates (), such that , which is an eigenfunction of with eigenvalues , . The radial function satisfies the equation

,

where . This has the form of the unperturbed two-dimensional oscillator and has the solutions (unnormalized, using atomic units ):

, ,

where is an associated Laguerre polynomial. The corresponding energies are

.

Using atomic units and expressing in teslas (T), . The energy, expanded in powers of the magnetic field, is then given by

.