Arizona developing first petahertz-speed phototransistor

26 May 2025

Offers route to computers millions of times faster than current ambient processors.

Researchers from the Department of Physics in the College of Science and the James C. Wyant College of Optical Sciences, all at the University of Arizona, have demonstrated a way to manipulate electrons in graphene using pulses of light that last less than a picosecond (10^-12 second). By leveraging a quantum effect known as tunneling, they recorded electrons bypassing a physical barrier almost instantaneously, a feat that they say “ redefines the potential limits of computer processing power.”

The achievement is described in a paper in Nature Communications, which highlights how the technique could lead to processing speeds in the petahertz range – over 1,000 times faster than modern computer chips.

Sending data at those speeds would revolutionize computing as we know it, said Mohammed Hassan, an associate professor of physics and optical sciences. Hassan has long pursued light-based computer technology and previously led efforts to develop the world's fastest electron microscope.

‘Huge leap forward’

“We have experienced a huge leap forward in the development of technologies like artificial intelligence software, but the speed of hardware development does not move as quickly,” Hassan said. “By leaning on the discovery of quantum computers, we can develop hardware that matches the current revolution in information technology software.”

Hassan worked alongside Arizona colleagues Nikolay Golubev, Mohamed Sennary, Jalil Shah, and Mingrui Yuan. They were joined by colleagues from the California Institute of Technology’s Jet Propulsion Laboratory and the Ludwig Maximilian University of Munich in Germany.

The team was originally studying the electrical conductivity of modified samples of graphene. When a laser shines on graphene, the energy of the laser excites electrons in the material, making them move and form into a current.

Sometimes, those electric currents cancel each other out. Hassan said this happens because the laser's energy wave moves up and down, generating equal and opposite currents on either side of the graphene. Because of graphene's symmetrical atomic structure, these currents mirror each other and cancel each other out, leaving no detectable current.

But what if a single electron could slip through the graphene, and its journey could be captured and tracked in real time? That near-instant tunnelling was the unexpected result of the team modifying different graphene samples.

“That is what I love most about science: The real discovery comes from the things you don't expect to happen,” Hassan said. “Going into the lab, you always anticipate what will happen – but the real beauty of science are the little things that happen, which lead you to investigate more. Once we realized that we had achieved this tunneling effect, we had to find out more.”

Using a commercially available graphene phototransistor that was modified to introduce a special silicon layer, the researchers used a laser that switches off and on at a rate of 638 attoseconds (638 x 10^-18s) to create what Hassan called “the world's fastest petahertz quantum transistor.”

Hassan is working with Tech Launch Arizona, the office that works with investigators to commercialize inventions stemming from Arizona research in order to patent and market innovations. While the original invention used a specialized laser, the researchers are furthering development of a transistor compatible with commercially available equipment.