Fig. 2: Phase transition in the isolated anti-PT symmetric dimer defect.
From: Observation of parity-time symmetry for evanescent waves
a Real (red circles) and imaginary (blue circles) parts of the experimentally obtained eigenvalues \({\lambda }_{1,2}^{({APT})}\) (in units of \(\kappa\)) for the passive anti-PT-symmetric dimer defect, alongside theoretical curves, versus resonant frequency detuning \(\triangle\). The light green region indicates the symmetric phase, while the light blue region represents the symmetry-broken phase. Measured (symbols) and fitted (curves) excitation spectra (b) and relative phase (c) of the cavities \(\pm\) within the dimer defect. The sound source for the excitation is positioned in cavity \(+\), and the system parameters are \(\gamma ={\kappa }_{r}=\kappa \sqrt{5}/2\), \(\triangle /{\kappa }_{r}=1\) and \({\triangle }_{0}={\omega }_{c}+3\kappa /2\), with \(\kappa /2{{{\rm{\pi }}}}=9\,{{{\rm{Hz}}}}\) and \({\omega }_{c}/2{{{\rm{\pi }}}}=1606\,{{{\rm{Hz}}}}\).
