Time- and frequency-domain polariton interference

We present experimental observations of interference between an atomic spin coherence and an optical field in a Lambda-type gradient echo memory. The interference is mediated by a strong classical field that couples a weak probe field to the atomic coherence through a resonant Raman transition. Interference can be observed between a prepared spin coherence and another propagating optical field, or between multiple Lambda transitions driving a single-spin coherence. Our scheme can behave as a controllable time-delayed beamsplitter with dynamically tuneable splitting ratio and allows, in principle, for unity interference visibility.