  Quantum state coherent frequency conversion processes-such as Bragg
scattering four wave mixing (BSFWM)-hold promise as a flexible technique for
networking heterogeneous and distant quantum systems. In this letter, we
demonstrate BSFWM within an extended (1.2-m) low-confinement silicon nitride
waveguide and show that this system has the potential for near unity quantum
coherent frequency conversion in visible and near-visible wavelength ranges.
Using sensitive heterodyne laser spectroscopy at low optical powers, we
characterize the Kerr coefficient (~1.55 W^{-1} m^{-1}) and linear propagation
loss (~0.0175 dB/cm) of this non-resonant waveguide system, revealing a
record-high nonlinear figure of merit (NFM = gamma/alpha is approximately equal
to 3.85 W^{-1}) for BSFWM of near visible light in non-resonant silicon nitride
waveguides. We demonstrate how, at high yet achievable on-chip optical powers,
this NFM would yield a comparatively large frequency conversion efficiency,
opening the door to near-unity flexible frequency conversion without cavity
enhancement and resulting bandwidth constraints.
