Demonstration of Returning Thouless Pump in a Berry Dipole System

Abstract

<p>The Thouless pump, a cornerstone of topological physics, enables unidirectional quantized wave or particle<br>transport via geometric Berry phase engineering in periodically driven systems. While decades of research<br>have been dedicated to monopole-mediated pumping, mechanisms governed by higher-order singularities like<br>Berry dipoles remain unexplored. Here, we report on the experimental demonstration of a Berry-dipolemediated<br>returning Thouless pump (RTP) in a 1D acoustic waveguide array achieved through adiabatic<br>encircling of a Berry dipole singularity. During this adiabatic cycle, an initial edge-localized mode first<br>delocalizes into the bulk and eventually returns to the original edge, marking the characteristic signature of the<br>RTP. Notably, thisRTP exhibits an interesting feature of pseudospin flipping. The demonstratedRTP contrasts<br>sharply with the well-studied monopole-governed pumps that feature unidirectional transport.<br></p>