  Precise measurement of the angular deviation of an object is a common task in
science and technology. Many methods use light for this purpose. Some of these
exploit interference effects to achieve technological advantages, such as
amplification effects, or simplified measurement devices. However, all of these
schemes require phase stability to be useful. Here we show theoretically and
experimentally that this drawback can be lifted by utilizing two-photon
interference, which is known to be less sensitive to phase fluctuations. Our
results show that non-classical interference can provide a path towards robust
interferometric sensing, allowing for increased metrological precision in the
presence of phase noise.
