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High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy
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Photoswitchable exceptional points derived from bound states in the continuum
Lei Wang1, Hang Liu1, Junwei Liu1
1Research Institute of Superconductor Electronics (RISE), Key Laboratory of Optoelectronic Devices and Systems with Extreme Performances of MOE, School of Electronic Science and Engineering, Nanjing University, Nanjing, 210023, China.
Light, Science & Applications
|October 29, 2025
Summary
This study reveals the transition from bound states in the continuum (BICs) to exceptional points (EPs) in non-Hermitian systems. These findings enable dynamic switching and terahertz beam deflection for advanced sensing and control devices.
Area of Science:
- Non-Hermitian physics
- Metasurfaces
- Terahertz technology
Background:
- Bound states in the continuum (BICs) and exceptional points (EPs) are critical singularities in non-Hermitian systems.
- Both phenomena have overlapping applications in sensing and lasers.
- The transition and interplay between BICs and EPs remain underexplored.
Purpose of the Study:
- To investigate the transition process from BICs to EPs in a non-Hermitian two-mode system.
- To experimentally validate the formation of an exceptional ring from quasi-Friedrich-Wintgen BICs.
- To demonstrate dynamic control and applications of this transition.
Main Methods:
- Theoretical analysis of a non-Hermitian two-mode system.
- Experimental realization using patterned dielectric metasurfaces in the terahertz band.
- Utilizing external pumping to induce photocarriers and control eigenfrequencies.
Main Results:
- Observed transition from a bound singularity to a 2D exceptional ring.
- Experimental validation of the EP as a coalescent state of quasi-FW-BICs.
- Demonstrated dynamic switching of EPs and switchable terahertz beam deflection.
Conclusions:
- The study elucidates the BIC-EP transition in non-Hermitian systems.
- Experimental validation confirms the theoretical predictions.
- Findings pave the way for novel terahertz devices for sensing and wavefront control.
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