New topological metamaterial amplifies sound waves exponentially


First representative of a so-called "bosonic kitaev chain" with potential to improve sensor technologies and information processing

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Publication in Nature:

J. J. Slim, C. C. Wanjura, M. Brunelli, J. del Pino, A. Nunnenkamp, and E. Verhagen
Optomechanical realization of a bosonic Kitaev chain
Nature 627, 767-771 (2024)
DOI: 10.1038/s41586-024-07174-w


The fermionic Kitaev chain is a canonical model featuring topological Majorana zero modes. We report the experimental realization of its bosonic analogue in a nano-optomechanical network, in which the parametric interactions induce beam-splitter coupling and two-mode squeezing among the nanomechanical modes, analogous to hopping and p-wave pairing in the fermionic case, respectively. This specific structure gives rise to a set of extraordinary phenomena in the bosonic dynamics and transport. We observe quadrature-dependent chiral amplification, exponential scaling of the gain with system size and strong sensitivity to boundary conditions. All these are linked to the unique non-Hermitian topological nature of the bosonic Kitaev chain. We probe the topological phase transition and uncover a rich dynamical phase diagram by controlling interaction phases and amplitudes. Finally, we present an experimental demonstration of an exponentially enhanced response to a small perturbation. These results represent the demonstration of a new synthetic phase of matter whose bosonic dynamics do not have fermionic parallels, and we have established a powerful system for studying non-Hermitian topology and its applications for signal manipulation and sensing.



Illustration of the bosonic Kitaev chain: Several mechanical string resonators are connected to form a chain with the aid of light.

Mechanical vibrations (sound waves) are transported along the chain and amplified. This phenomenon is an expression of non-trivial non-Hermitian topology. C: Ella Maru Studio