Nanoscale trick makes “dark excitons” glow 300,000 times stronger

Dark excitons form in ultra-thin semiconductor materials and normally remain undetectable because they release only faint light. Even so, scientists have long viewed them as promising for quantum information and advanced photonics because they interact with light in unusual ways, remain stable for relatively long periods, and experience less disruption from their surroundings, which helps reduce decoherence.

Amplifying Dark Excitons With Nanoscale Design

To bring these hidden states into view, the researchers created a tiny optical cavity built from gold nanotubes combined with a single layer of tungsten diselenide (WSe2), a material just three atoms thick. This structure increased the brightness of dark excitons by an extraordinary factor of 300,000, making them clearly observable and allowing their behavior to be precisely controlled.

"This work shows that we can access and manipulate light-matter states that were previously out of reach," said principal investigator Andrea Alù, 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."

Electric and Magnetic Control of Hidden Quantum States

The team also demonstrated that these dark excitons can be switched and adjusted using electric and magnetic fields. This level of control could support new designs for on-chip photonics, highly sensitive detectors, and secure quantum communication. Importantly, the method preserves the original characteristics of the material while still achieving record-setting improvements in light-matter coupling.

"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 Debate in Plasmonics

The findings also address a long-standing question of whether plasmonic structures can boost dark excitons without altering their fundamental nature when placed in close proximity. The researchers solved this by designing a plasmonic-excitonic heterostructure made with nanometer-thin boron nitride layers, which proved essential for revealing the newly identified dark excitons.

The work received support from the Air Force Office of Scientific Research, the Office of Naval Research, and the National Science Foundation.