As modern computers approach their physical limits, semiconductor components currently operate at maximum frequencies of just a few gigahertz, performing billions of computing operations per second. To maintain performance, systems often rely on multiple chips to distribute tasks, as the speed of individual chips cannot be further increased. However, a game-changing leap in speed could be achieved if photons (light) were used instead of electrons (electricity) in computer chips, potentially making them up to 1000 times faster.
A promising approach to unlocking this leap in speed is through plasmonic resonators, often called “antennas for light.” These nanometer-sized metal structures allow for interaction between light and electrons, and their performance can vary depending on their geometry. “The challenge,” says Dr. Thorsten Feichtner, a physicist at Julius-Maximilians-Universität (JMU) Würzburg in Germany, “is that plasmonic resonators cannot yet be modulated effectively, unlike transistors in conventional electronics. This limitation prevents the development of fast, light-based switches.”
However, a collaborative research team from JMU and the Southern Denmark University (SDU) in Odense has made a major breakthrough in this area. They have developed an electrically controlled modulation of plasmonic resonators, paving the way for ultra-fast active plasmonics and significantly faster computer chips. Their findings were recently published in Science Advances.
Instead of altering the entire resonator, the research team focused on modifying its surface properties. This key advancement was made possible by electrically contacting a single resonator, specifically a nanorod made of gold. Though conceptually simple, this technique required sophisticated nanofabrication using helium ion beams and gold nanocrystals. This unique fabrication method was developed at the JMU Chair of Experimental Physics under the guidance of Professor Bert Hecht. In addition, precise measurement techniques involving a lock-in amplifier were essential for detecting the subtle but critical effects on the resonator’s surface.
Dr. Feichtner explains, “The effect we’re leveraging is similar to the Faraday cage principle. Just as electrons in a car struck by lightning collect on the outside, protecting those inside, additional electrons on the surface affect the optical properties of the resonators.” Traditionally, optical antennas were understood through classical mechanics: electrons in metal stopped at the nanoparticle’s edge, like water meeting a harbor wall. However, measurements by the Würzburg team showed changes in resonance that could no longer be explained by classical physics. Instead, electrons “smear” across the boundary between metal and air, creating a soft transition like a sandy beach meeting the sea.
To interpret these quantum effects, theorists at SDU developed a semi-classical model, incorporating quantum properties into surface parameters, allowing calculations using classical methods. “By perturbing the surface’s response functions, we merge classical and quantum effects, advancing our understanding of surface dynamics,” explains JMU physicist Luka Zurak, the study’s first author.
While the new model successfully reproduces the experimental results, the specific quantum effects at the metal surface remain unclear. “For the first time, we can now design antennas with precision and amplify or exclude individual quantum effects,” says Feichtner.
In the future, the researchers anticipate even more potential applications. Smaller resonators could lead to highly efficient optical modulators, which would have technological uses. Additionally, the system they developed could provide new insights into energy conversion and storage technologies by investigating the influence of surface electrons in catalytic processes.
This breakthrough opens a new frontier for quantum research and holds the promise of revolutionizing the speed and efficiency of future computer chips.
By Impact Lab
