Lead by Andrea Alú, CUNY.

For instance, topological protection against scattering, a key property for the design of low loss TA wave devices, exploits (a) the orthogonality of counter-propagating waves resulting from breaking inversion symmetry of pseudospin TA waves, and (b) the absence of a counter-propagating waves resulting from breaking time-reversal symmetry of TA waves. While the second type of topologically protected wave is more robust than the first type, its practical physical implementation is more challenging due to the need to inject energy into the system. NewFoS will explore other symmetry breaking strategies (e.g., translational symmetry) to achieve robust immunity to backscattering in TA structures that can be realized in passive systems.

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Lead by Chiara Daraio, Caltech.

Non-symmetry breaking topological order may arise in strongly correlated systems even if there is an apparent lack of long-range order as measured by local order parameters. This phenomenon has been essentially associated with topological order in quantum systems such as spin lattices. NewFoS will explore classical strongly correlated nonlinear acoustic systems that can lead to behaviors analogous to the quantum topological ordered phases. This research will open new avenues to investigating emergent topological phenomena resulting from nonlinear correlations. These phenomena will offer revolutionary paths to developing acoustic analogues of topological qubits and novel approaches to robust massively parallel information processing.

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Lead by Massimo Ruzzene, UCB.

Among the topological properties of sound that have recently been uncovered, a few have emerged that are highly sensitive to parametric changes of governing physical properties. Beyond phase, which is thoroughly explored in project 3, exceptional points generated by the introduction of balanced gain and loss have attracted significant interest for potential sensing applications. The use of exceptional points to develop new sensing modalities is an open area of research which can be explored in the context of NewFos. The investigation of changes in an acoustic cavity or in an acoustic medium can leverage the interrogation of exceptional points and can lead to new concepts of relevant to a variety of fields, such as assessment of the mechanical properties of cells, to the detection of damage or, more generally, heterogeneities in structural components. In addition, the study of acoustic waves generated by complex frequency excitation and their interaction with heterogeneities and impedance mismatched interfaces can be also studied in the context of topology, leading to analogies related to time inversion symmetries, PT symmetries and non-Hermitian dynamics. These investigations are also likely to lead to novel concepts for sensing and for new ultrasound imaging strategies.

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