Entanglement and Optical Nonreciprocity in spontaneous Raman Scattering

Inelastic light scattering is a central tool for sample characterization and label-free imaging across the physical and life sciences.

Recent work has suggested that scattered light can also exhibit nonclassical correlations.

Here, we develop a microscopic theory of Raman scattering that connects naturally to established descriptions of entangled-photon generation in three- and four-wave mixing, while capturing essential differences arising from the resonant, dissipative character of Raman scattering.

Using a cumulant-expansion approach, we analyze the entanglement structure of the scattered sidebands and identify signatures that distinguish Raman-mediated correlations from those generated in conventional off-resonant nonlinear wave mixing.

In particular, we show that Raman scattering induces chiral couplings between Stokes and anti-Stokes sidebands, leading to nonreciprocal amplification of coherent seed fields.

These results establish a theoretical framework for Raman-based quantum photonic protocols and suggest routes toward quantum-enhanced Raman spectroscopy and imaging.