  Scalable photonic quantum technologies are based on multiple nested
interferometers. To realize this architecture, integrated optical structures
are needed to ensure stable, controllable, and repeatable operation. Here we
show a key proof-of-principle demonstration of an externally-controlled
photonic quantum circuit based upon UV-written waveguide technology. In
particular, we present non-classical interference of photon pairs in a
Mach-Zehnder interferometer constructed with X couplers in an integrated
optical circuit with a thermo-optic phase shifter in one of the interferometer
arms.
