An outstanding challenge for deployable quantum technologies is the
availability of high-resolution laser spectroscopy at the specific wavelengths
of ultranarrow transitions in atomic and solid-state quantum systems. Here, we
demonstrate a powerful spectroscopic tool that synergistically combines high
resolution with flexible wavelength access, by showing that nonlinear
nanophotonics can be readily pumped with electro-optic frequency combs to
enable highly coherent spectral translation with essentially no efficiency
loss. Third-order (\c{hi}(3)) optical parametric oscillation in a silicon
nitride microring enables nearly a million optical frequency comb pump teeth to
be translated onto signal and idler beams; while the comb tooth spacing and
bandwidth are adjustable through electro-optic control, the signal and idler
carrier frequencies are widely tuneable through dispersion engineering. We then
demonstrate the application of these devices to quantum systems, by performing
sub-Doppler spectroscopy of the hyperfine transitions of a Cs atomic vapor with
our electro-optically-driven Kerr nonlinear light source. The generality,
robustness, and agility of this approach as well as its compatibility with
photonic integration are expected to lead to its widespread applications in
areas such as quantum sensing, telecommunications, and atomic clocks.Comment: 17 pages, 5 figure