Analysis and experiment of multiple exceptional points in reconfigurable synthetic anti-PT symmetric hybrid system

Non-Hermitian systems such as parity-time (PT) and anti-PT (APT) symmetric systems have generated great interest owing to their unique property of exhibiting real eigenvalues in open environments. This study presents a reconfigurable synthetic anti-PT symmetric hybrid (ASH) system that can control eigenstates to achieve multiple exceptional points (EPs). A distinct feature of the proposed system is that it is based on a hybrid structure, which combines dissipative and coherent couplings. To implement dissipative coupling, a bidirectional negative-impedance converter is proposed using a symmetric coupling element. This approach easily achieves a matched amplification rate, significantly simplifying the design of the ASH system. A phase diagram is used to illustrate the evolution and coalescence of multiple EPs when the system parameters vary. This diagram reveals four distinct regions defined by critical EP boundaries. Phase rigidity is also used to investigate the evolution of spectral singularities and eigenmode mixing. Experimental results show good agreement with theoretical calculations, which demonstrates a real and coupling-independent eigenfrequency when the broken symmetry phases vanish. This study extends the design space of APT symmetric systems, offering a reconfigurable platform for practical implementations of EP-based devices and applications.