  Control over the coupling between multiple modes of a frequency comb is an
important step toward measurement-based quantum computation with a
continuous-variable system. We demonstrate the creation of square-ladder
correlation graphs in a microwave comb with 95 modes. The graphs are engineered
through precise control of the relative phase of three pumps applied to a
Josephson parametric oscillator. Experimental measurement of the mode
scattering matrix is in good agreement with theoretical predictions based on a
linearized equation of motion of the parametric oscillator. The digital methods
used to create and measure the correlations are easily scaled to more modes and
more pumps, with the potential to tailor a specific correlation graph topology.
