Efficient cryogenic nonlinear conversion processes in periodically-poled thin-film lithium niobate waveguides

Periodically poled thin-film lithium niobate (TFLN) waveguides, which enable efficient quadratic nonlinear processes, serve as crucial foundation for classical and quantum signal processing. To expand their application scope, we provide the first investigation of nonlinear conversion processes in periodically poled TFLN waveguides at cryogenic condition (7 K). Through systematic experimental characterization, we find that the periodically poled TFLN waveguide retains its high conversion efficiency at both cryogenic and room temperatures for both classical second-harmonic generation and quantum photon-pair generation processes. Particularly, the photon-pair source at cryogenic condition shows high brightness and broad bandwidth. These results demonstrate the significant potential of TFLN wavelength conversion devices for cryogenic applications and foster future scalable quantum photonic systems.