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Telecom quantum light sources such as quantum dots, as well as weak coherent laser pulses have recently been gaining importance for quantum repeater applications, by entangling the photons with quantum memory nodes, possessing long spin coherence times [1]. However, since most of the quantum memories exhibit an optical interface in the visible or near-infrared, telecom-to-visible quantum frequency conversion is crucial for long-distance quantum entanglement distribution.
Here, we present a two-stage conversion scheme to tune single telecom photons to resonance with the tin-vacancy (SnV) center in diamond in a fiber-integrated design using a solid-core photonic crystal fiber (PCF) coupled to a periodically-poled lithium niobate (PPLN) waveguide. The signal photons at 1550 nm are converted to 619 nm in a two-step sum-frequency generation process using a strong pump field at 2062 nm. This fiber-integrated design offers increased robustness against fluctuations of ambient conditions, paving the way for operation outside of a controlled lab environment. We show results on fiber-to-waveguide coupling as well as conversion efficiencies.
[1] Knaut, C.M. et al., Nature 629, 573–578