PhD defense: Ilia Chernobrovkin

Valley-Hall Topological Phononic Waveguides in Mesoscopic Membrane Resonators

Experimental realizations of exotic physical phenomena have the potential to enhance the performance of the existing technology and bring forward new applications. Low-loss information transport is particularly interesting for both classical and quantum systems. One particular approach is rooted in the field of topology, which predicts the existence of propagation channels that are protected from scattering by the geometry of the host platform itself.

This work discusses a specific case of topological insulators based on the principles of Valley-Hall physics. This phenomenon was first observed in electronic two-dimensional systems and lately has been applied to optical and acoustic fields. However, all realizations of topological phononic waveguides suffer from large dissipation rates intrinsic to the base materials.

We attempt to combat this limitation by introducing the Valley-Hall topology into the Si₃N₄ mesoscopic membrane resonator platform. By applying the techniques of dissipation dilution and soft-clamping, we enhance the waveguide performance and observe the propagation loss rate as low as 3.1 dB/km. This property allows us to characterize scattering at sharp bends, which is supposed to be suppressed by the geometrical symmetry of the device. We observe that at every waveguide corner about 99.99% of the phononic field is transmitted through.

In addition to that, we also explore the potential for inducing nonlinearities in topological systems, and propose a fast imaging protocol that is able to resolve sub-wavelength phase-dependent features of vibrational displacement fields.

Zoom link: https://ucph-ku.zoom.us/j/63480060385?pwd=gKRuPraxILixJ5g1N981rz5fj8wiOX.1