Researchers have reached a breakthrough in ultrafast optical switching using atomically thin materials
Scientists in Germany and the UK have demonstrated an ultrafast light-switching mechanism using a nanostructure made from silver and an atomically thin semiconductor
The advance could pave the way for optical components that operate up to 10,000 times faster than today’s electronic transistors, offering new possibilities for data processing, sensing and quantum technologies.
The research, led by physicists at the University of Oldenburg and published in Nature Nanotechnology, shows how light can be controlled on timescales of just a few femtoseconds by carefully engineering interactions between light and matter at the nanoscale.
A hybrid nanostructure with unusual properties
A central part of the experiment is a hybrid nanostructure that combines two materials with very different properties. Researchers fabricated an ultra-thin silver “nano-slit array” by milling a grid of parallel grooves, each only around 45 nanometres wide and deep, into the metal’s surface.
On top of this structure, collaborators from the University of Cambridge placed a monolayer of tungsten disulfide, a semiconductor crystal just three atoms thick.
Neither the silver nanostructure nor the semiconductor layer shows any significant switching behaviour individually. When combined, however, the system behaves as an “active metamaterial,” exhibiting optical properties not found in nature. The interaction between the two materials fundamentally alters how light behaves at the surface.
Trapping light in a quantum hybrid state
When light hits the hybrid nanostructure, it does not immediately reflect. Instead, it becomes temporarily stored in a hybrid quantum state known as an exciton-plasmon polariton.
This state blends properties of light and matter, allowing the energy to travel across the surface as plasmon waves while strongly interacting with excitons in the semiconductor layer.
This storage phase lasts for roughly 70 femtoseconds. During that extremely brief interval, the researchers were able to manipulate the amount of light that would eventually be reflected by the surface. By using an additional laser pulse, they altered the interaction strength between excitons and plasmon waves, effectively switching the material’s reflectivity.
In initial experiments, the brightness of the reflected light could be changed by up to 10 per cent, a surprisingly large effect at such ultrafast timescales. Further improvements are expected as the materials and nanostructure design are optimised.
Filming electron motion in real time
To observe this rapid switching process, the team employed two-dimensional electronic spectroscopy, a sophisticated technique that allows scientists to track quantum interactions with femtosecond resolution. Recent methodological advances have enabled probing the metamaterial with laser pulses even shorter than the switching process itself.
This approach allowed the researchers to reconstruct the different stages of the light-matter interaction, as if it were a high-speed film.
What this means for future technologies
Ultrafast nanoscale optical switches could dramatically increase the amount of information transmitted per unit of time. Conventional electronic transistors switch on timescales that are thousands of times slower, placing fundamental limits on computing speed.
Optical technologies offer a route beyond these limits, potentially enabling faster computers, more efficient chip manufacturing, highly sensitive optical sensors and new architectures for quantum computing. Achieving these applications will depend on further advances in the design and control of active metamaterials, such as the one demonstrated in this study.
The work involved researchers from the University of Oldenburg, the University of Cambridge, the Politecnico di Milano and Technische Universität Berlin, highlighting the increasingly international nature of research at the frontiers of nanophysics and photonics.
