Selective enhancement of topologically induced interface states in a dielectric resonator chain.

Charles Poli,Matthieu Bellec,Ulrich Kuhl,Fabrice Mortessagne,Henning Schomerus

doi:10.1038/ncomms7710

Abstract

The recent realization of topological phases in insulators and superconductors has advanced the search for robust quantum technologies. The prospect to implement the underlying topological features controllably has given incentive to explore optical platforms for analogous realizations. Here we realize a topologically induced defect state in a chain of dielectric microwave resonators and show that the functionality of the system can be enhanced by supplementing topological protection with non-hermitian symmetries that do not have an electronic counterpart. We draw on a characteristic topological feature of the defect state, namely, that it breaks a sublattice symmetry. This isolates the state from losses that respect parity-time symmetry, which enhances its visibility relative to all other states both in the frequency and in the time domain. This mode selection mechanism naturally carries over to a wide range of topological and parity-time symmetric optical platforms, including couplers, rectifiers and lasers.

Highlights

The recent realization of topological phases in insulators and superconductors has advanced the search for robust quantum technologies
The topological defect state has been observed in a quantum walk scenario[12], while a dimer chain with a non-topological defect has been realised in a waveguide array[14]
The topological features of the PTsymmetric variant of the chain without a defect has been discussed in[20,21], while two recent experiments have exploited spontaneous PT-symmetry breaking for mode selection in a laser[22,23]

Summary

Introduction

The recent realization of topological phases in insulators and superconductors has advanced the search for robust quantum technologies. A key element for the intended topological functionality are robust confined states that form at interfaces between regions with topologically distinct band structures For electromagnetic waves, this can be realized in two-dimensions by breaking symmetries in analogy to the quantum Hall effect[4,5,6] or the quantum spin Hall effect[7,8,9], while in one-dimension one can employ lattice modulations[10,11,12]. This can be realized in two-dimensions by breaking symmetries in analogy to the quantum Hall effect[4,5,6] or the quantum spin Hall effect[7,8,9], while in one-dimension one can employ lattice modulations[10,11,12] Concerning the latter setting, a minimal one-dimensional model with a topological band structure is a chain of sites with alternating couplings (that is, a dimer chain). Besides its relevance for mode guiding and filtering, as well as rectifiers and couplers exploiting passive PT symmetry, this mechanism lays the conceptual ground for selecting a topologically induced state in mode competition in active variants of the symmetry, tying it to the topical problem of gain–loss enabled lasing

Methods

Results

Conclusion