  We experimentally investigate the formation of subradiant atomic momentum
states in Bose-Einstein condensates inside a recoil resolving optical ring
resonator according to the theoretical proposal of Cola, Bigerni, and Piovella.
The atoms are pumped from the side with laser light that contains two frequency
components. They resonantly drive cavity assisted Raman transitions between
three discreet atomic momentum states. Within a few hundred microseconds, the
system evolves into a stationary subradiant state. In this state, the
condensate develops two density gratings suitable to diffract the two frequency
components of the pump field into the resonator. Both components destructively
interfere such that scattering is efficiently suppressed. A series of
subradiant states for various amplitude ratios of the two pump components
between 0 and 2.1 have been observed. The results are well explained with a
three state quantum model in mean field approximation.
