Fig. 3
Eigensystem structure of an APT-symmetric circuit. a, b Real and imaginary eigenvalues inferred from the resonance-excitation spectra in Fig. 2b in comparison with theory. The theoretical curves are obtained by a binary Hamiltonian model derived from Kirchhoff’s circuit laws. The shaded area for ε/κ > 1 indicates the parametric region of the broken PT-symmetry (PTS) phase. c State amplitude ratio v1/v2 as a function of the energy-detuning parameter ε, where vn denotes complex amplitude of the state vector |v〉 such that |v〉 = [v1 v2]T. Circles indicate experimentally obtained values and dashed curves are obtained from the binary Hamiltonian model. The upper inset panels show corresponding eigenvector |λ±〉 coordinates on the Gauss plane for ε = 0, 0.5κ, κ, and 1.5κ
