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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. In 2001, Knill, Laflamme and Milburn (KLM) proposed an efficient scheme for linear optical quantum computing [1]. The KLM proposal is based upon a probabilistic, two-qubit, Controlled NOT (CNOT) gate along with local unitary operations on individual qubits. Some years later, Okamoto, et. al., demonstrated experimentally a realization the KLM CNOT gate in bulk optics [2]. The KLM CNOT gate, shown schematically in Fig. (1), is itself composed of two Non-Linear Phase Shift Gates (NLPSG), the essential two-qubit element of the CNOT gate. Each NLPSG is a probabilistic device involving three optical modes, that, in the bulk optical realization encounter strategically placed and optimally reflective beam splitters that appropriately route the free space evolution of photonic states through the system. The KLM CNOT gate performs a two qubit operation, namely, a flip of the target qubit (t) conditioned on the value of the control qubit (c), as CNOT c t c t i j i i j    .

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At the composition 31.6 at. % gold, the equilibrium diagram shows a two-phase mixture of ordered and disordered material extending from 320°C to 350°C. However, a long anneal in this interval results in an x-ray pattern showing superstructure reflections with strong satellites. The satellite pattern is obtained both by lowering and raising the temperature, and hence is believed to represent an equilibrium structure. The satellite pattern is interpreted in terms of a Cu3Au II type structure, which is derived from the ordered Cu3Au I by introducing antiphase domain displacements (a2+a3)/2 at regular intervals along the a1 axis, exactly analogous to the development of CuAu II from CuAu I. At 31.6 at. % gold, the period is 18a1 (9 a1 between consecutive domain boundaries). Between 320°C and 335°C, there is a two-phase mixture of Cu3Au I and Cu3Au II. From 335°C to about 345°C the structure is that of Cu3Au II. From about 345°C to 350°C there is probably a two-phase mixture of Cu3Au II and disordered material, but this has not been established. The satellite pattern is also obtained at the composition 29.2 at. % gold, and it is likely that the Cu3Au II type structure exists over a range of compositions on the gold rich side of Cu3Au.