  The design, fabrication, and detailed calibration of essential building
blocks towards fully integrated linear-optics quantum computation are
discussed. Photonic devices are made from silicon nitride rib waveguides, where
measurements on ring resonators show small propagation losses. Directional
couplers are designed to be insensitive to fabrication variations. Their offset
and coupling lengths are measured, as well as the phase difference between the
transmitted and reflected light. With careful calibrations, the insertion loss
of the directional couplers is found to be small. Finally, an integrated
controlled-NOT circuit is characterized by measuring the transmission through
different combinations of inputs and outputs. The gate fidelity for the CNOT
operation with this circuit is estimated to be 99.81% after post selection.
This high fidelity is due to our robust design, good fabrication
reproducibility, and extensive characterizations.
