  We consider to detect the electron spin of a doped atom, i.e., a nitrogen or
a phosphorus, caged in a fullerene by currently available technique of the
scanning tunneling microscope (STM), which actually corresponds to the readout
of a qubit in the fullerene-based quantum computing. Under the conditions of
polarized STM current and Coulomb blockade, we investigate the tunneling matrix
elements involving the exchange coupling between the tunneling polarized
electrons and the encapsulated polarized electron, and calculate the variation
of the tunneling current with respect to different orientations of the
encapsulated electron spin. The experimental feasibility of our scheme is
discussed under the consideration of some imperfect factors.
