  The aim of this paper is to study the q-Laplace operator and q-harmonic
polynomials on the quantum complex vector space generated by z_i,w_i,
i=1,2,...,n, on which the quantum group GL_q(n) (or U_q(n)) acts. The
q-harmonic polynomials are defined as solutions of the equation Delta_qp=0,
where p is a polynomial in z_i,w_i, i=1,2,...,n, and the q-Laplace operator
Delta_q is determined in terms of q-derivatives. The q-Laplace operator Delta_q
commutes with the action of GL_q(n). The projector H_{m,m'}: A_{m,m'} -->
H_{m,m'} is constructed, where A_{m,m'} and H_{m,m'} are the spaces of
homogeneous (of degree m in z_i and of degree m' in w_i) polynomials and
homogeneous q-harmonic polynomials, respectively. By using these projectors, a
q-analogue of the classical zonal spherical and associated spherical harmonics
are constructed. They constitute an orthogonal basis of H_{m,m'}. A q-analogue
of separation of variables is given. The quantum algebra U_q(gl_n), acting on
H_{m,m'}, determines an irreducible representation of U_q(gl_n). This action is
explicitly constructed. The results of the paper lead to the dual pair
(U_q(sl_2), U_q(gl_n)) of quantum algebras.
