  We report photonic quantum circuits created using an ultrafast laser
processing technique that is rapid, requires no lithographic mask and can be
used to create three-dimensional networks of waveguide devices. We have
characterized directional couplers--the key functional elements of photonic
quantum circuits--and found that they perform as well as lithographically
produced waveguide devices. We further demonstrate high-performance
interferometers and an important multi-photon quantum interference phenomenon
for the first time in integrated optics. This direct-write approach will enable
the rapid development of sophisticated quantum optical circuits and their
scaling into three-dimensions.
