Non-Weyl Behavior Induced by Superradiance: A Microwave Graph Study

TL;DR

This study experimentally investigates how superradiance induces non-Weyl behavior in microwave graphs by varying boundary conditions, revealing resonance dynamics and transitions in open systems.

Contribution

It introduces a novel method to control coupling in microwave graphs, enabling observation of superradiant transitions and non-Weyl behavior in open quantum systems.

Findings

Resonances escape via superradiant transition under balanced coupling.

Resonance spectra exhibit loops and regions of resonance connection.

Open tetrahedral graph shows complex resonance dynamics with infinite imaginary parts.

Abstract

We study experimentally the manifestation of non-Weyl graph behavior in open systems using microwave networks. For this a coupling variation to the network is necessary, which was out of reach till now. The coupling to the environment is changed by indirectly varying the boundary condition at the coupling vertex from Dirichlet to Neumann using a dangling bond with variable length attached the coupling vertex. A transformation of equal length spectra to equal reflection phase spectra of the dangling bond allows to create spectra with different fixed coupling strength. This allows to follow the resonances in the complex plane as a function of the coupling. While going from closed (Dirichlet) to fully open (Neumann) graph we see resonances escaping via a superradiant transition leading to non-Weyl behavior if the coupling to the outside is balanced. The open tetrahedral graph displays a rich parametric dynamic of the resonances in the complex plane presenting loops, regions of connected resonances and resonances approaching infinite imaginary parts.