Super-resolving frequency measurement with mode-selective quantum memory

Abstract: High-precision optical frequency measurement is indispensable to modern science and technology, yet conventional spectroscopic techniques struggle to resolve spectral features narrower than their bandwidth. Here, we introduce a unique platform for super-resolving frequency estimation utilizing a mode-selective atomic Raman quantum memory implemented in warm cesium vapor. By precisely engineering the light-matter interaction, our memory coherently stores the optimal temporal mode with high fidelity and retrieves it on-demand, realizing a mode crosstalk as low as 0.34%. For the task of estimating the separation between two spectral lines, we experimentally measure the mean squared error of the frequency estimate, achieving a sensitivity as small as 1/20 of the linewidth with up to a ($34\pm4$)-fold enhancement in precision over direct intensity measurements. This enhanced resolution of frequency measurements, combined with the memory's capability of on-demand storage, retrieval and mode conversion, paves the way for multifunctional memory-based time-frequency sensors and their integration within quantum networks.