Towards quantum metrology for nanoscatterers

Measurements play a pivotal role in the advance of science and technology. To name just two examples, the global positioning system (GPS) technology relies on atomic clocks, and the detection of gravitational waves has been achieved via extremely precise interferometric measurements. The aim of my thesis is to contribute towards the goal of doing quantum metrology with nanophotonic structures. With this motivation, some problems across the fields of nanophotonics and quantum optics are tackled. First, the role of helicity within nanophotonics is explored. In the context of symmetries and conserved quantities, helicity, the projection of the total angular momentum on the linear momentum direction, is a useful addition to the more commonly considered quantities such as angular momentum. A simple but versatile experimental treatment of helicity is introduced and demonstrated on the scattering of focused light by circular nanoholes in a gold film. The helicity transformation that takes place in this light-matter interaction is studied. Another section is devoted to the topic of quantum light sources. It is shown how to influence and measure the spectrotemporal wave function of photon pairs by exploiting properties of the spontaneous parametric down-conversion (SPDC) process. The proposed technique also allows to determine the distribution of time delays between the two photons in a pair, which is typically a challenging experimental task. Finally, a quantum metrology experiment on the interaction of light with chiral molecules is presented. In this proof-of-concept experiment entangled photon pairs are used for the measurement of natural optical activity and its wavelength dependence, the optical rotatory dispersion.