  Integrated photonics promises solutions to questions of stability,
complexity, and size in quantum optics. Advances in tunable and non-planar
integrated platforms, such laser-inscribed photonics, continue to bring the
realisation of quantum advantages in computation and metrology ever closer,
perhaps most easily seen in multi-path interferometry. Here we demonstrate
control of two-photon interference in a chip-scale 3D multi-path
interferometer, showing a reduced periodicity and enhanced visibility compared
to single photon measurements. Observed non-classical visibilities are widely
tunable, and explained well by theoretical predictions based on classical
measurements. With these predictions we extract a Fisher information
approaching a theoretical maximum, demonstrating the capability of the device
for quantum enhanced phase measurements.
