Exceptional Points of PT-Symmetric Reflectionless States in Complex Scattering Systems

Area of Science:

• Complex wave scattering
• Non-Hermitian physics
• Quantum mechanics

Background:

• Reflectionless (RL) states offer unique wave-scattering properties.
• Exceptional points (EPs) in parity-time (PT)-symmetric systems represent critical points where eigenvalues and eigenvectors coalesce.
• Understanding RL states and EPs is crucial for advancing wave phenomena and device functionalities.

Purpose of the Study:

• To experimentally and analytically investigate the coalescence of reflectionless (RL) states in symmetric complex wave-scattering systems.
• To identify and characterize RL exceptional points (EPs) in different scattering configurations.
• To explore the application of RL and RL-EP states in analog signal processing.

Main Methods:

• Experimental observation of RL EPs in a conventional Fabry-Perot system with tunable scattering strength.
• Investigation of RL EPs in single- and multichannel symmetric disordered systems.
• Analytical confirmation of EP conditions for PT-symmetric RL operators using quasinormal modes.
• Leveraging transfer functions for analog differentiation.

Main Results:

• Observation of RL exceptional points (EPs) in both Fabry-Perot and disordered symmetric complex wave-scattering systems.
• Confirmation that an EP of the PT-symmetric RL operator occurs when the central frequency spacing equals the decay rate.
• Successful implementation of first- and second-order analog differentiation using RL and RL-EP states.

Conclusions:

• The coalescence of RL states leads to observable EPs in various symmetric complex wave systems.
• The identified condition for PT-symmetric RL EPs provides a pathway for their controlled generation.
• RL-EP states offer a promising platform for developing novel analog signal processing devices.