Researchers made a significant step towards creating ultrafast computers.

The long-standing goal of science and technology is to create electronic and information processing systems that run at the speed of nature.

This promising method involves using laser light to guide electrons through matter and then using this control for electronic circuit elements. This is known as lightwave electronics.

Amazingly, current lasers can generate electricity bursts in fractions of a second, that is, one millionth of a trillionth of a second. Yet our capacity to process information at such ultrafast timescales has remained elusive.Now, researchers at the University of Rochester and the Friedrich-Alexander-Universitat Erlangen-Nurnberg (FAU) have made a decisive step in this direction by demonstrating a logic gate–the building block of computation and information processing–that operates at femtosecond timescales. This feat was published in the journal Nature on May 11. It involved harnessing and controlling for the first times the virtual and real charge carriers that make these lightning fast bursts.

Researchers’ breakthroughs have made it possible to process information at the petahertz limit. This means that one quadrillion computations can be performed per second. This is nearly a million times faster that computers running at gigahertz clock speeds, where 1 petahertz equals 1 million gigahertz.

“This is an excellent example of how fundamental science may lead to new technologies,” said Ignacio Franco (associate professor of chemistry at Rochester), who in collaboration with Antonio Jose Garzon Ramirez ’21 (PhD), conducted the theoretical studies that led to this discovery.

Lasers produce lightning fast bursts electricity

Scientists have been able to harness laser pulses lasting only a few seconds to produce ultrafast bursts electrical currents. For example, tiny graphene-based wires that connect two gold metals can be illuminated. The laser pulse is short and sets in motion the electrons in graphene. It also sends them in a specific direction, generating an electrical current.

Laser pulses are able to produce electricity much faster than traditional methods, and they can do this without any applied voltage. You can also control the current’s direction and magnitude by simply changing the phase of the laser pulse.

The breakthrough: Harnessing virtual and real charge carriers

Franco’s research group and Peter Hommelhoff from FAU have worked for many years to transform light waves into ultrafast pulses.

The team came to a realization while trying to reconcile experimental measurements from Erlangen with computer simulations from Rochester: It is possible to produce two flavors of gold-graphene/gold junctions. These are the particles that carry the charge responsible for these bursts.

• These “Real” charges are electrons that have been excited by light and remain in directional motion after the laser pulse has been turned off.
• “Virtual charge carriersare electrons set in net directional motion during the laser pulse. They are an elusive species and only exist for a short time during illumination.

The graphene is connected with gold so both real and imaginary charge carriers are absorbed by it to create a net current. However, the team found that they could change the shape of the laser pulse to generate currents in which only the real charge carriers or virtual charge carriers play a part. They not only created two types of currents but also learned how to control them individually, which greatly enhances the design elements in lightwave electronics.

Lasers as logic gates

This augmented control environment allowed the team to demonstrate logic gates that operate in a fraction of a second using this experimental landscape.

The basic building blocks of computation are logic gates. They control the processing of incoming information. This information can take the form of bits (or 0) or a combination thereof. Two input signals are required for logic gates to produce a logic output.

The input signals in the experiment are the phase or shape of two synchronized laser pulses. Each pulse is chosen to generate a burst or real charge carrier. These two contributions can add up or cancel each other depending on which laser phases were used. You can assign the net electrical signal logical information 0, or 1, which will produce an ultrafast logic gate.

Tobias Boolakee was a FAU PhD student who led the experiments. “It will likely be a long time before this technology can be used in computer chips, but at least now we know that lightwave electronic is practicable,” he said.