  We report the successful design and experimental implementation of three
coincident nonlinear interactions, namely ZZZ ("type-0"), ZYY (type-I), and
YYZ/YZY (type-II) second harmonic generation of 780 nm light from a 1560 nm
pump beam in a single, multigrating, periodically poled KTiOPO_4 crystal. The
resulting nonlinear medium is the key component for making a scalable quantum
computer over the optical frequency comb of a single optical parametric
oscillator.
