Several proposals have been recently introduced to implement Quantum Machine Learning (QML) algorithms for the analysis of classical data sets employing variational learning means. There has been, however, a limited amount of work on the characterization and analysis of quantum data by means of these techniques, so far. This work focuses on one such ambitious goal, namely the potential implementation of quantum algorithms allowing to properly classify quantum states defined over a single register of$n$qubits, based on their degree of entanglement. This is a notoriously hard task to be performed on classical hardware, due to the exponential scaling of the corresponding Hilbert space as 2n. We exploit the notion of “entanglement witness”, i.e., an operator whose expectation values allow to identify certain specific states as entangled. More in detail, we made use of Quantum Neural Networks (QNNs) in order to successfully learn how to reproduce the action of an entanglement witness. This work may pave the way to an efficient combination of QML algorithms and quantum information protocols, possibly outperforming classical approaches to analyse quantum data. All these topics are discussed and properly demonstrated through a simulation of the related quantum circuit model.

The dispersion of photonic modes in one-dimensional (1-D) and two-dimensional (2-D) patterned silicon-on-insulator (SOI) waveguides, also containing line defects, is fully investigated both above and below the light line. Quasi-guided (radiative), as well as truly guided modes are probed by means of angle- and polarization-resolved microreflectance and attenuated total reflectance measurements. For the 1-D case, the sharp resonances observed in reflectance spectra are analyzed in terms of the Airy-Fano model, and the measured linewidths are shown to be very close to theoretical predictions. In the 2-D lattices containing W1 line defects the presence of a supercell repetition leads to the simultaneous excitation of defect and bulk modes which are folded in a reduced Brillouin zone. The measured dispersion is in very good agreement with full three-dimensional calculations based on expansion on the waveguide modes, indicating that a deep understanding of the propagation properties of patterned SOI waveguides is achieved.