  We present a scheme for robust and efficient projection measurement of a
qubit consisting of the two magnetic sublevels in the electronic ground state
of alkali earth metal ions. The scheme is based on two stimulated Raman
adiabatic passages (STIRAP) involving four partially coherent laser fields. We
show how the efficiency depends on experimentally relevant parameters: Rabi
frequencies, pulse widths, laser linewidths, one- and two-photon detunings,
residual laser power, laser polarization and ion motion.
