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Microwave experiments on atypical transport phenomena induced by spatial and spectral wave shaping

Thèse Julian Böhm

à 13h30 en salle C. BROT

Transport of waves plays an important role in modern communication systems like Wi-Fi or optical fibres. Typical problems in such systems concern security against possible intruders, energy consumption, time efficiency and the possibility of mode filtering. Microwave experiments are suited to study this kind of problems, because they offer a good control of the experimental parameters like sub-wavelength precision or phase and amplitude adjustment of the signals. Thus we can implement the method of wave shaping to investigate atypical transport phenomena, which address the mentioned problems.

Wave front shaping solely based on the transmission together with the Wigner-Smith time delay formalism allows me to establish special scattering states in situ. These scattering states avoid a pre-selected region, focus on a specific spot or follow trajectories of classical particles, so called particle-like scattering states. Energy efficient transport and avoiding possible intruders are the most interesting features of these states.

Mode filtering is induced inside a waveguide with wavy boundaries and position dependent loss. The boundary profiles are chosen in such a way that the two propagating modes describe an encircling of an exceptional point in the Bloch picture. The asymmetric mode filtering is found due to the non-adiabatic transitions occurring during this encircling. This is the first experimental realisation of a dynamical encircling of an exceptional point.

Another part of my work deals with Grover’s quantum search. I put such a search into practice in a two-dimensional graphene-lattice using coupled resonators, which form a tight-binding analogue. In this proof of principle experiment we search for different resonators attached to the graphene-lattice. Changing the transmission direction of the signal according to the initially shaped wave can be seen as a graphene based switch. Furthermore, the scaling behaviour of the quantum search is quantified for a linear chain of resonators.