  Adiabatic frequency conversion has some key advantages over nonlinear
frequency conversion. No threshold and no phase-matching conditions need to be
fulfilled. Moreover, it exhibits a conversion efficiency of $100\,\%$ down to
the single-photon level. Adiabatic frequency conversion schemes in
microresonators demonstrated so far suffer either from low quality factors of
the employed resonators resulting in short photon lifetimes or small frequency
shifts. Here, we present an adiabatic frequency conversion (AFC) scheme by
employing the Pockels effect. We use a non-centrosymmetric ultrahigh-$Q$
microresonator made out of lithium niobate. Frequency shifts of more than
$5\,$GHz are achieved by applying just $20\,$V to $70$-micrometer-thick
crystal. Furthermore, we demonstrate that already with the same setup positive
and a negative frequency chirps can be generated. With this method, by
controlling the voltage applied to the crystal, almost arbitrary frequency
shifts can be realized. The general advances in on-chip fabrication of
lithium-niobate-based devices make it feasible to transfer the current
apparatus onto a chip suitable for mass production.
