Spatial Spin-Wave Modulator for Quantum-Memory-Assisted Adaptive Measurements

Use of the spatial degree of freedom vastly enhances the informational capacity of light at the cost of stringent requirements on the processing devices. Multimode quantum memories are a viable candidate for quantum and classical information processing; however, full use of the assets of high-dimensionality requires a flexible processing technique. We use a spatially varying ac Stark effect to perform arbitrary one-dimensional phase modulation of a coherent spin-wave state stored in a wavevector-multiplexed quantum memory. A far-field characterization and an interferometric near-field characterization of the introduced phase profiles are presented. Additionally, coherence between temporally separated partial readouts of a single coherent spin-wave state is demonstrated, offering possible applications in adaptive measurements via conditional spin-wave modulation.