Attosecond phase spectroscopy of semiconductor quantum wells

Summary form only given. Irreversible absorption of light in any material requires that the coherence of the initial photoexcited state be lost. In quantum-engineered semiconductor systems, decoherence cannot be treated merely phenomenologically, and coherent phenomena play a dramatic role, even in the linear optical properties. We have devised an ultrafast coherent spectroscopy that directly tracks the evolution of the electron-hole phase after excitation with a laser pulse. In high-quality quantum well samples, this general technique uncovers a coherent response differing strongly from that observed on incoherent excitation.