Non-Hermitian Josephson junctions with four Majorana zero modes

TL;DR

This paper explores how non-Hermitian effects influence Josephson junctions with four Majorana zero modes, revealing exceptional points and spectral features relevant for topological quantum devices.

Contribution

It introduces the study of non-Hermitian effects in Majorana-hosting Josephson junctions, highlighting the formation of Andreev exceptional points and their spectral signatures.

Findings

Formation of Andreev exceptional points depending on non-Hermitian coupling

Strong local and nonlocal spectral weights at exceptional points

Potential for conductance-based identification of non-Hermitian effects

Abstract

Josephson junctions formed by finite-length topological superconductors host four Majorana zero modes when the phase difference between the superconductors is $\varphi=\pi$ and their length is larger than the Majorana localization length. While this picture is understood in terms of a Hermitian description of isolated junctions, unavoidable transport conditions due to coupling to reservoirs make them open and ground for non-Hermitian effects that still remain largely unexplored. In this work, we investigate the impact of non-Hermiticity on Josephson junctions hosting four Majorana zero modes when they are coupled to normal leads. We demonstrate that, depending on whether inner or outer Majorana zero modes are subjected to non-Hermiticity, Andreev exceptional points can form between lowest (higher energy) Andreev bound states connected by stable zero real energy lines. We further find that the Andreev exceptional points give rise to strong local and nonlocal spectral weights, thus providing a way for their identification via, e.g., conductance measurements. Our findings unveil non-Hermiticity for designing non-Hermitian topological phases and for operating Andreev bound states in Josephson junctions hosting Majorana zero modes.