Cyclic Population Transfer in Quantum Systems with Broken Symmetry

We show that quantum systems with broken symmetry can be selectively excited due to the coexistence of one- and two-photon transitions between the same states. Discrimination between two mirror-symmetric quantum wells or left- and right-handed chiral molecules can be accomplished by a ``cyclic population transfer'' process, in which one optically couples three system states |1〉↔|2〉↔|3〉↔|1〉, and completely transfers population from state $|1〉$ to state $|2〉$ and |3〉M (i.e., state $|3〉$ of the mirror imaged system) or state $|3〉$ and |2〉M, depending on the laser phases.