Abstract
Zero-energy particles (such as Majorana fermions) are newly predicted quasiparticles and are expected to play an important role in fault-tolerant quantum computation. In conventional Hermitian quantum systems, however, such zero states are vulnerable and even become vanishing if couplings with surroundings are of the same topological nature. Here we demonstrate a robust photonic zero mode sustained by a spatial non-Hermitian phase transition in a parity-time (PT) symmetric lattice, despite the same topological order across the entire system. The non-Hermitian-enhanced topological protection ensures the reemergence of the zero mode at the phase transition interface when the two semi-lattices under different PT phases are decoupled effectively in their real spectra. Residing at the midgap level of the PT symmetric spectrum, the zero mode is topologically protected against topological disorder. We experimentally validated the robustness of the zero-energy mode by ultrafast heterodyne measurements of light transport dynamics in a silicon waveguide lattice.
Highlights
IntroductionZero-energy particles (such as Majorana fermions) are newly predicted quasiparticles and are expected to play an important role in fault-tolerant quantum computation
Zero-energy particles are newly predicted quasiparticles and are expected to play an important role in fault-tolerant quantum computation
The non-Hermitian phase transition creates a zero-energy mode, which retains some topological protection but that would be prevented in the Hermitian limit
Summary
Zero-energy particles (such as Majorana fermions) are newly predicted quasiparticles and are expected to play an important role in fault-tolerant quantum computation. Among the investigated robust states, the dimensionless-bound state with its eigen energy pinned at the middle of a gapped band structure is referred to as the zero mode[10,11] Examples of such zero-energy modes are the selfconjugated Majorana-bound states in px + ipy superconductors[11] that are regarded as the promising braiding anyons for the protective non-Abelian statistics, enabling fault-tolerant quantum error correction and computation[1,2,3,4,5]. One extreme configuration is to bring next to the defect site a crystal with exactly the same topological order, which eliminates the interface completely and the topological zero mode We address this challenge by demonstrating the existence of a genuine non-Hermitian topological defect state, despite the coupling of the defect mode to the surroundings with the same topological order. As a result of the non-Hermitian quantum phase transition, intriguing topological characteristics, such as the zero energy and topologically protected robustness against perturbations, are recovered
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