Observation of topological transport quantization by dissipation in fast Thouless pumps

Zlata Fedorova,Johann Kroha,Stefan Linden,Haixin Qiu

doi:10.1038/s41467-020-17510-z

Abstract

Quantized dynamics is essential for natural processes and technological applications alike. The work of Thouless on quantized particle transport in slowly varying potentials (Thouless pumping) has played a key role in understanding that such quantization may be caused not only by discrete eigenvalues of a quantum system, but also by invariants associated with the nontrivial topology of the Hamiltonian parameter space. Since its discovery, quantized Thouless pumping has been believed to be restricted to the limit of slow driving, a fundamental obstacle for experimental applications. Here, we introduce non-Hermitian Floquet engineering as a new concept to overcome this problem. We predict that a topological band structure and associated quantized transport can be restored at driving frequencies as large as the system’s band gap. The underlying mechanism is suppression of non-adiabatic transitions by tailored, time-periodic dissipation. We confirm the theoretical predictions by experiments on topological transport quantization in plasmonic waveguide arrays.

Highlights

Quantized dynamics is essential for natural processes and technological applications alike
Such nontrivial topology of the Hamiltonian parameter space or band structure was recognized as the overarching concept behind phenomena apparently as diverse as the integer quantum Hall effect[4], the quantum spin Hall effect[5], topological insulators in solid state[6] and photonics[7,8], quantum spin[9] or charge pumping[1], Dirac or Weyl semimetals[10], and the electric polarization of crystalline solids[11]
Realistic experimental systems are to some extent open and subject to dissipation, so that the quantum mechanical time evolution of single-particle states deviates from unitarity, which may prevent the closing of the cycle in Hamiltonian parameter space

Summary

Introduction

Quantized dynamics is essential for natural processes and technological applications alike. Realistic experimental systems are to some extent open and subject to dissipation, so that the quantum mechanical time evolution of single-particle states deviates from unitarity, which may prevent the closing of the cycle in Hamiltonian parameter space. This motivates the interest in non-Hermitian (NH) Hamiltonians. DLSPPWs are uniquely suited model systems for realizing topological transport with dissipation: The propagation of surface plasmon polaritons mathematically realizes the singleparticle Schrödinger equation on a one-dimensional tight-binding lattice[30,31], where the waveguide axis resembles time, and the system parameters, including losses, can be modulated along the waveguide axis. This is essential for probing the band topology which otherwise is possible only in fermionic systems at low temperature

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