Copyright Interesting Engineering
Researchers at the City University of New York (CUNY) and the University of Texas at Austin have achieved a breakthrough in manipulating one of the most elusive phenomena in modern optics – dark excitons. By finding a way to make these previously hidden light states shine brightly and controllably, the team has opened a new frontier for faster, smaller, and more energy-efficient technologies. Dark excitons are exotic light-matter states found in atomically thin semiconductors. They usually remain invisible because they emit light very weakly. Yet, their long lifetimes and low interaction with the environment make them ideal for quantum information and sensing applications. To expose these hidden states, the research team engineered a nanoscale optical cavity made of gold nanotubes and a single layer of tungsten diselenide (WSe₂), a material only three atoms thick. This precise setup amplified light emission from dark excitons by nearly 300,000 times. The enhancement made them not only visible but also controllable at the nanoscale. “This work shows that we can access and manipulate light-matter states that were previously out of reach,” said Andrea Alù, the study’s principal investigator and Distinguished and Einstein Professor of Physics at the CUNY Graduate Center. Alù also directs the Photonics Initiative at the Advanced Science Research Center at CUNY. He added that the ability to switch these states on and off with nanoscale precision could drive major advances. “By turning these hidden states on and off at will and controlling them with nanoscale resolution, we open exciting opportunities to disruptively advance next-generation optical and quantum technologies, including for sensing and computing.” Precision control with electric fields The team went further by showing that dark excitons could be tuned on demand using electric and magnetic fields. This level of control allows fine-tuning of their emission properties for use in on-chip photonics, sensors, and secure quantum communication. Unlike earlier efforts that modified material properties, this new approach preserves the semiconductor’s natural characteristics. It achieves record-breaking enhancement in light-matter coupling without compromising the integrity of the material. “Our study reveals a new family of spin-forbidden dark excitons that had never been observed before,” said first author Jiamin Quan. “This discovery is just the beginning—it opens a path to explore many other hidden quantum states in 2D materials.” Solving a long-standing mystery The discovery also resolves a debate within the nanophotonics community. Scientists have long questioned whether plasmonic structures could enhance dark excitons without altering their intrinsic nature. The CUNY–UT Austin team answered that by designing a precise plasmonic-excitonic heterostructure. They used nanometer-thin layers of boron nitride to separate the gold and semiconductor materials. This delicate layering maintained the excitons’ quantum behavior while amplifying their emission. The research received support from the Air Force Office of Scientific Research, the Office of Naval Research, and the National Science Foundation. By turning “dark” light states into controllable, shining phenomena, the study marks a leap toward quantum systems that are smaller, faster, and far more efficient than today’s optical technologies. The study is published in the journal Nature Photonics.
