Researchers at City University of New York and University of Texas at Austin have made previously invisible “dark excitons” shine by amplifying their light emission 300,000 times using gold nanotubes and tungsten diselenide (WSe₂) just three atoms thick.
Published in Nature Photonics, the breakthrough enables nanoscale control of these exotic light-matter states through electric and magnetic fields, opening pathways for quantum communication and ultra-compact photonic devices, according to Andrea Alù, Distinguished and Einstein Professor at CUNY Graduate Center.
A research team at the City University of New York and the University of Texas at Austin has discovered a way to make previously hidden states of light, known as dark excitons, shine brightly and control their emission at the nanoscale. Their findings, published today in Nature Photonics, open the door to faster, smaller, and more energy-efficient technologies.
Dark excitons are exotic light-matter states in atomically thin semiconductors that typically remain invisible because they emit light very weakly. These states, however, are highly promising for quantum information and advanced photonic applications due to their unique light-matter interaction properties, long lifetimes and reduced interaction with the environment, which leads to lessened decoherence.
To reveal these elusive states, the team engineered a nanoscale optical cavity using gold nanotubes and a single layer of tungsten diselenide (WSe₂), a material just three atoms thick. This design amplified the light emission from dark excitons by an astonishing 300,000 times, making them not only visible but also controllable.
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“This work shows that we can access and manipulate light-matter states that were previously out of reach,” said the study’s principal investigator Andrea Alù, who is a Distinguished and Einstein Professor of Physics at the CUNY Graduate Center and founding director of the Photonics Initiative at the Advanced Science Research Center at the CUNY Graduate Center (CUNY ASRC).
“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.”
The research team also demonstrated that these dark states can be tuned on demand using electric and magnetic fields, enabling precise control for potential applications in on-chip photonics, sensors, and quantum communication. Unlike previous attempts, this approach preserves the material’s natural properties while achieving record-breaking enhancement of light-matter coupling.
“Our study reveals a new family of spin-forbidden dark excitons that had never been observed before,” said Jiamin Quan, first author of the study. “This discovery is just the beginning—it opens a path to explore many other hidden quantum states in 2D materials.”
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Understanding what makes this breakthrough significant requires grasping what dark excitons are and why they matter. When light interacts with atomically thin semiconductors, it can create bound pairs of electrons and holes called excitons.
Most excitons readily emit light and are called “bright excitons.” Dark excitons, however, have quantum properties that prevent them from easily releasing photons, making them effectively invisible to conventional optical detection.
This invisibility paradoxically makes dark excitons valuable. Their reluctance to emit light means they interact weakly with their environment, giving them longer lifetimes and better coherence—critical properties for quantum computing and communication where maintaining quantum states proves challenging.
The problem has always been accessing and controlling these hidden states. The CUNY-UT Austin team solved this through precise nanoengineering. By sandwiching the three-atom-thick WSe₂ layer between gold nanotubes and using nanometer-thin layers of boron nitride as spacers, they created an optical cavity that dramatically enhances light-matter coupling specifically for dark excitons.
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The 300,000-fold amplification represents a quantum leap—quite literally—over previous efforts. This level of enhancement makes dark excitons not just visible but practical for device applications. More importantly, the team demonstrated tunability: applying electric and magnetic fields allows researchers to turn these states on and off and control their properties with precision.
This discovery also resolves a long-standing debate about whether plasmonic structures—materials that support collective oscillations of electrons—can truly enhance dark excitons without altering their fundamental nature as they come in close contact.
The authors addressed the challenge by carefully designing the plasmonic-excitonic heterostructure using nanometer-thin layers of boron nitride, key to unveiling the new dark excitons observed by the team.
The practical applications span multiple cutting-edge fields. In quantum communication, controllable dark excitons could serve as quantum bits (qubits) that maintain coherence longer than current alternatives. For ultra-compact photonic devices, the ability to manipulate light-matter interactions at the nanoscale enables components orders of magnitude smaller than conventional optics.
Sensing applications could leverage the dark excitons’ sensitivity to external fields. Even minute changes in electric or magnetic environments would alter their emission properties, potentially enabling detection of single molecules or tiny magnetic field variations. Computing applications might use these states to create optical switches and logic gates operating at quantum scales.
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The materials involved—tungsten diselenide and similar two-dimensional semiconductors—belong to a family of materials only atoms thick yet with rich electronic and optical properties. These materials have emerged as platforms for exploring exotic quantum phenomena, and the current work expands the accessible physics dramatically.
The work was supported by the Air Force Office of Scientific Research, the Office of Naval Research, and the National Science Foundation, reflecting the technology’s potential military and civilian applications.
