Gain and loss induced topological insulating phase in a non Hermitian electrical circuit

TL;DR

This paper demonstrates an experimental 1D non-Hermitian topological electrical circuit where gain and loss induce topologically protected edge states, with tunable phases and robust impedance signatures, advancing controllable topological systems.

Contribution

It introduces a practical electrical circuit platform for non-Hermitian topological phases, showing gain/loss induced topological states and phase switching via resistor tuning.

Findings

Observation of topologically protected edge states at circuit edges.

Switching between topological phases by resistor tuning.

Impedance peaks indicating robust edge and interface states.

Abstract

There have been considerable efforts devoted to the study of topological phases in certain non-Hermitian systems that possess real eigenfrequencies in the presence of gain and loss. However, it is challenging to experimentally realize such non-Hermitian topological insulators in either quantum or photonic systems, due to the difficulties in introducing controlled gain and loss. On the other hand, the wide choices of active circuit components provide us with unprecedented convenience and flexibility in engineering non-Hermitian topological insulators in electrical circuits. Here, we report experimental realization of a one-dimensional (1D) non-Hermitian topological circuit which exhibits topologically protected edge state purely induced by gain and loss. We show that by tuning the value of the positive/negative resistors in the circuit, our system can switch between different topological phase regions. The topological edge states and interface states are observed at the circuit edge and at the interface between a trivial and nontrivial circuit, which are manifested by a prominent impedance peak at the mid-gap frequency topologically robust to variations of circuit parameters. Our work opens a new gateway towards actively controllable topological systems.