Abstract

Recently, there have been several advancements in the development of sources for narrowband non-classical light (with linewidth ≲ MHz). This is motivated by applications in quantum information and sensing where quantum light is interfaced with material quanta such as atoms or molecules. For instance, photonic quantum information processing can be realised through strong photon-photon interactions mediated by non-linearity in atoms and requires photon-pairs in which both photons are resonant and matched in bandwidth to an atomic transition. Applications in quantum networking, e.g. entanglement-swapping with memory-compatible photons, require the photons to be pure and indistinguishable in addition to being matched in frequency and bandwidth to quantum memories. Cavity-enhanced spontaneous parametric downconversion (CE-SPDC) - a robust technique to produce bright nar-rowband photon pairs [1]- has enabled advancements such as reduction of photon bandwidth to the kHz range, frequency conversion while preserving non-classical correlations in a pair, and independent frequency tuning of each photon in an entangled pair with MHz precision [2].

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