  We present a practical method for active phase control on a photonic chip
that has immediate applications in quantum photonics. Our approach uses
strain-optic modification of the refractive index of individual waveguides,
effected by a millimeter-scale mechanical actuator. The resulting phase change
of propagating optical fields is rapid and polarization-dependent, enabling
quantum applications that require active control and polarization encoding. We
demonstrate strain-optic control of non-classical states of light in silica,
showing the generation of 2-photon polarisation N00N states by manipulating
Hong-Ou-Mandel interference. We also demonstrate switching times of a few
microseconds, which are sufficient for silica-based feed-forward control of
photonic quantum states.
