  We propose a simple and effective way of creating pure dark superposition
states. The generation of pure states is carried out by using bichromatic
radiation with controllable polarization ellipticity. We derived analytic
formulas for polarization elipticity to obtain pure dark states of different
Zeeman sublevels of alkali atoms. Experimentally we accumulated ~60% of the
atoms in the 0-0 dark state of the D1 line of Rb87
