Reviewed by Lexie CornerApr 2 2025
In a study published in the journal Science, researchers from Florida International University and the Advanced Science Research Center at the CUNY Graduate Center (CUNY ASRC) present their findings on complex frequencies excitations, a newly proposed method to manipulate light, sound, and other wave phenomena beyond traditional limitations.
This methodology offers opportunities to enhance the understanding of wave-matter interactions and advance wave-based technology.
Control over wave phenomena in conventional light and sound systems, such as in wireless communication, microscopes, speakers, and earphones, is limited by the intrinsic properties of the materials used. Overcoming these limitations typically requires the use of exotic materials, additional energy input, or more complex equipment.
Complex frequency excitations present an alternative approach to improving wave control using conventional materials. By modifying the excitation form to oscillate at complex-valued frequencies, rather than altering the materials themselves, it is possible to simulate the presence of gain and loss in the system.
This approach enables access to non-Hermitian responses, perfect absorption, super-resolution imaging, and the bypassing of passivity limitations in wave-matter interactions, without the need for energy-intensive and unstable active components.
This approach provides a fundamentally new strategy for wave control. We are no longer limited by the material platform to enhance the device performance. We can now shape how wave-based systems respond simply by designing the right kinds of excitations.
Andrea Alù, Study Principal Investigator and Distinguished Professor and Einstein Professor, The City University of New York Graduate Center
Alù is also the founding director of the CUNY ASRC Photonics Initiative.
A New Frontier in Wave Physics
The research team’s study demonstrates how, under certain conditions, signal excitations with amplitudes that grow or decay exponentially over time can interact with a system's natural resonances and anti-resonances. This interaction simulates the effects of precisely introducing distributions of material gain and/or loss. Potential applications include enhanced quantum state control, directional wave transmission, signal absorption and amplification, and dynamic light control.
Led by Alù’s team, the research represents some of the first investigations in this field, highlighting advancements in wireless power transfer, super-resolution imaging, controlled energy storage, and wave modification beyond passivity limits.
Increased control over wave phenomena could lead to improved medical imaging, more efficient wireless communication systems, and better manipulation of wave-based quantum states, which would benefit applications in quantum sensing and computing.
While the initial demonstrations of complex-frequency excitations have been limited to radio and acoustic frequencies, scaling this technique to higher frequencies, such as optical systems, remains a challenge. Our work lays the foundation for future breakthroughs by providing a roadmap for researchers across various wave physics domains to explore the untapped potential of complex frequency excitations.
Seunghwi Kim, Study First Author and Postdoctoral Researcher, The City University of New York Graduate Center
Researchers from Florida International University's Department of Electrical and Computer Engineering and the CUNY ASRC Photonics Initiative collaborated on the study.
Journal Reference:
Kim, S. et. al. (2025) Complex-frequency excitations in photonics and wave physics. Science. doi.org/10.1126/science.ado4128