Quantum Plasmonic Tunnelling Circuits Ten Thousand times Faster than Today’s Microprocessors

two plasmonic resonators bridged by a layer of molecules Electrical circuits which are able to operate at hundreds of terahertz frequencies (tens of thousands times faster than today’s state-of-the-art microprocessors), have been successfully developed by scientists in Singapore.

The breakthrough could potentially revolutionize high-speed electronics, nanoscale opto-electronics and nonlinear optics. It uses a novel process named quantum plasmonic tunnelling.

By altering the molecules in the molecular electronic device, frequency of circuits can be altered in the hundreds of terahertz range.

The new circuits may possibly be used in applications to construct ultra-fast computers or single molecule detectors in the future. New possibilities in nano-electronic devices could also be opened up.

Photonics and Nano-scale Devices

In fibre optical cables, light is used as an information carrier and transmitted. Photonic components are bulky but operate at tremendously high frequencies of 100 terahertz, about 10,000 times faster than the desktop computer.

Current state-of-the-art nano-electronic devices, however, operate at much smaller scales, making it highly challenging to unite the ultra-fast properties of photonic elements with nano-scale electronics.

It has long been known by scientists that light is able to interact with certain metals and can be captured in the form of plasmons, which are collective, ultra-fast oscillations of electrons that can be manipulated at the nano-scale.

The so-called quantum plasmon modes have been theoretically predicted to occur at atomic length scales. But even today’s state-of-the-art fabrication techniques can only reach length scales that are about five nanometre larger, so quantum-plasmon effects have been hard to investigate.

Plasmonic Resonators

For this study, the researchers team showed that quantum plasmonics is actually possible at length scales that are useful for real applications. Researchers successfully created an element of a molecular electronic circuit using two plasmonic resonators, which are structures that can capture light in the form of plasmons, bridged by a layer of molecules that is exactly one molecule thick.

The layer of molecules switches on the quantum plasmonic tunneling effects, allowing the circuits to operate at terahertz frequencies.

Dr Michel Bosman of Singapore’s Agency for Science, Technology and Research used an advanced electron microscopy technique to see and measure the opto-electronic properties of these structures with nanometer resolution.

These measurements demonstrated the existence of the quantum plasmon mode and that its speed could be controlled by varying the molecular properties of the devices.

“We are very excited by the new findings”, Asst Prof Nijhuis said. “Our team is the first to observe the quantum plasmonic tunneling effects directly. This is also the first time that a research team has demonstrated theoretically and experimentally that very fast-switching at optical frequencies are indeed possible in molecular electronic devices.”


S. F. Tan, L. Wu, J. K. W. Yang, P. Bai, M. Bosman, C. A. Nijhuis.
Quantum Plasmon Resonances Controlled by Molecular Tunnel Junctions.
Science, 2014; 343 (6178): 1496 DOI: 10.1126/science.1248797

Image: Tan Shu Fen, National University of Singapore