The preparation, control, and measurement of non-classical states of light are necessary to realizing optical quantum technologies. The frequency of light – the photon energy or its wavelength – is one of its fundamental degrees of freedom, within which we can manipulate a quantum state: for example, we can imagine preparing photons in superpositions of various wavelengths; or entangling photons such that their energies correlate. In contrast to the other luminal degrees of freedom, however, modifying the energy of photons requires nonlinear optics. The greater difficulty that this introduces in implementing quantum state transformations and measurements has proven to be an obstacle to the development of experimental methods for frequency-domain quantum optics. However, frequency-domain engineering would allow us to leverage the breadth of optical bandwidths, hence is advantageous for parallel quantum state generation and information encoding. In addition, the preparation of squeezed vacuum – the most accessible non-classical optical state – already relies on a frequency conversion process. This implies that the ability to combine the preparation and transformation steps into a joint nonlinear process may greatly benefit the efficiency and fidelity of producing the final state. In this thesis I will present an experimental paradigm which uses ultrafast nonlinear optics and broadband frequency conversion techniques to enable the transformation and measurement of frequency-multimode squeezed vacuum states.