Observation of Acoustic Non-Hermitian Bloch Braids and Associated Topological Phase Transitions

Abstract

Topological features embedded in ancient braiding and knotting arts endow significant impacts on our daily life and even cutting-edge science. Recently, fast growing efforts are invested to the braiding topology of complex Bloch bands in non-Hermitian systems. This new classification of band topology goes far beyond those established in Hermitian counterparts. Here, we present the first acoustic realization of the topological non-Hermitian Bloch braids, based on a two-band model easily accessible for realizing any desired knot structure. The non-Hermitian bands are synthesized by a simple binary cavity-tube system, where the long-range, complex-valued, and momentum-resolved couplings are accomplished by a well-controlled unidirectional coupler. In addition to directly visualizing various two-band braiding patterns, we unambiguously observe the highly-elusive topological phase transitions between them. Not only do our results provide a direct demonstration for the non-Hermitian band topology, but also the experimental techniques open new avenues for designing unconventional acoustic metamaterials.

Accepted by PRL

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• Braid Protected Topological Band Structures with Unpaired Exceptional Points
• Generalized bulk-boundary correspondence in periodically driven non-Hermitian systems
• Experimental realization of stable exceptional chains protected by non-Hermitian latent symmetries unique to mechanical systems
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• Machine Learning of Knot Topology in Non-Hermitian Band Braids
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• Fully-Polarized Topological Isostatic Metamaterials in Three Dimensions
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• Direct measurement of topological invariants through temporal adiabatic evolution of bulk states in the synthetic Brillouin zone
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• Super-enhanced Sensitivity in Non-Hermitian Systems at Infernal Points
• Measuring Non-Hermitian Topological Invariants Directly from Quench Dynamics
• Observation of Braid-Protected Unpaired Exceptional Points
• A new class of higher-order topological insulators that localize energy at arbitrary multiple sites
• Topological Dynamics and Correspondences in Composite Exceptional Rings
• Pseudo-Hermitian Topology of Multiband Non-Hermitian Systems
• Implementation and topological characterization of Weyl exceptional rings in quantum-mechanical systems
• Experimentally Probing Non-Hermitian Spectral Transition and Eigenstate Skewness
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• Machine learning topological energy braiding of non-Bloch bands
• Entanglement manifestation of knot topology in a non-Hermitian lattice
• Braiding of dynamical eigenvalues of Hermitian bosonic Kitaev chains
• Non-Hermitian topology in a single driven-dissipative Kerr-Cat qubit
• Non-orientable Exceptional Points in Twisted Boundary Systems
• Exceptional topology on nonorientable manifolds
• Emergence of Nodal-Knot Transitions by Disorder
• Emergence of Hermitian topology from non-Hermitian knots