Exceptional nexus in Bose-Einstein condensates with collective dissipation

TL;DR

This paper experimentally demonstrates a third-order exceptional nexus in a dissipative Bose-Einstein condensate system, revealing complex topological phenomena and collective dissipation effects in many-body quantum systems.

Contribution

It introduces the first realization of an exceptional nexus in a three-state ultracold atomic system without symmetry constraints.

Findings

Successfully created an exceptional nexus in a BEC system

Observed coalescence of exceptional arcs with different geometries

Analyzed dissipation effects in strong coupling and quantum Zeno regimes

Abstract

In multistate non-Hermitian systems, higher-order exceptional points and exotic phenomena with no analogues in two-level systems arise. A paradigm is the exceptional nexus (EX), a third-order EP as the cusp singularity of exceptional arcs (EAs), that has a hybrid topological nature. Using atomic Bose-Einstein condensates to implement a dissipative three-state system, we experimentally realize an EX within a two-parameter space, despite the absence of symmetry. The engineered dissipation exhibits density dependence due to the collective atomic response to resonant light. Based on extensive analysis of the system's decay dynamics, we demonstrate the formation of an EX from the coalescence of two EAs with distinct geometries. These structures arise from the different roles played by dissipation in the strong coupling limit and quantum Zeno regime. Our work paves the way for exploring higher-order exceptional physics in the many-body setting of ultracold atoms.