  We propose a scalable version of a KLM CNOT gate based upon integrated
waveguide microring resonators (MRR), vs the original KLM-approach using beam
splitters (BS). The core element of our CNOT gate is a nonlinear phase-shift
gate (NLPSG) using three MRRs, which we examine in detail. We find an expanded
parameter space for the NLPSG over that of the conventional version. Whereas in
all prior proposals for bulk optical realizations of the NLPSG the optimal
operating point is precisely a single zero dimensional manifold within the
parameter space of the device, we find conditions for effective transmission
amplitudes which define a set of one dimensional manifolds in the parameters
spaces of the MRRs. This allows for an unprecedented level flexibility in
operation of the NLPSG that and allows for the fabrication of tunable MRR-based
devices with high precision and low loss.
