" The simplest form of pseudospin to enable topological sound relies on geometrical asymmetries, for example, an acoustic array of subwave-length resonators with carefully tailored asymmetries act like a spin on sound waves (Ni et al., 2018). The resulting devices are passive and support topological boundary sound waves somewhat robust to disorder.... Topological acoustic quantization, for example, based on two opposite pseudospins, coherence and correlations, can be harnessed to overcome stability and scalability challenges in current approaches to massive-data information processing, within the context of the second quantum revolution (Dowling and Milburn, 2003)."
Topological Acoustics by Pierre Deymer
"Elastic displacement measured with a laser vibrometer over a spatiotemporally modulated array of piezoelectric patches, demonstrating the emergence of a one-way topological boundary propagation of sound (Darabi et al., 2020). b: A topological mechanical metamaterial made of a three-dimensional printed elastic polymer based on asymmetric nonlinearities (Coulais et al., 2017)"