Experimental function estimation from quantum phase measurements

Characterizing and analyzing a system often requires learning an unknown function, such as the response of a system or the profile of a field. The standard approach is to opportunely sample the function at fiducial points and then interpolate. When the quantity of interest is embodied in physical objects accessible with quantum-enhanced measurements, it becomes relevant to investigate how to transfer this advantage from the individual sampled points to the estimation of the whole function. In this article we report the experimental quantum-enhanced function estimation of the optical response of a liquid crystal. Our results illustrate that optimizing the employment of the resources is not as straightforward as it may appear at a first glance: Quantum advantage becomes substantial only past a sampling density that depends on the interpolation method, and on the function at hand. Our results show how quantum resources should successfully be employed to access the rich information contained in continuous signals.