Laser Pulses for Ultrafast Signal Processing Could Make Computers a Million Times Faster

Illustration of the gold-graphene structure in which electron waves from real and virtual charges are targeted with two ultrafast laser pulses. The combined effect can be used in an ultra-fast logic gate. Photo credit: Michael Osadciw, University of Rochester

The simulation of complex scientific models on the computer or the processing of large amounts of data such as the editing of video material takes up a lot of computing power and time. Researchers from the Chair of Laser Physics at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) and a team from the University of Rochester in New York have shown how the speed of basic computing operations can be increased to up to a million times faster with laser pulses in the future. Their findings were published in the journal on May 11, 2022 Nature.

The computing speed of today’s computer and smartphone processors is given by field effect transistors. In the race to make faster devices, these transistors are constantly being reduced in size to fit as many as possible together on chips. Modern computers are already working at the breathtaking speed of several gigahertz, which corresponds to several billion arithmetic operations per second. The latest transistors are only 5 nanometers (0.000005 millimeters) in size, which is little more than a few atoms. Chip manufacturers are limited and at some point it will no longer be possible to make transistors smaller.

light is faster

Physicists are working flat out to control electronics with light waves. The oscillation of a light wave lasts about one femtosecond, that is one millionth of a billionth of a second. The control of electrical signals with light could make the computers of the future more than a million times faster, that is the goal of petahertz signal processing or light wave electronics.

From light waves to current pulses

Electronics serve to transmit and process signals and data in the form of logical information using binary logic (1 and 0). These signals can also be in the form of current pulses.

Researchers from the Chair of Laser Physics have investigated how light waves can be converted into current pulses several years. In their experiments, the researchers shed light on a structure of[{” attribute=””>graphene and gold electrodes with ultrashort laser pulses. The laser pulses induce electron waves in the graphene, which move toward the gold electrodes where they are measured as current pulses and can be processed as information.

Real and virtual charges

Depending on where the laser pulse hits the surface, the electron waves spread differently. This creates two types of current pulses which are known as real and virtual charges.

Tobias Boolakee

Tobias Boolakee. Credit: FAU/Johanna Hojer

“Imagine that graphene is a pool and the gold electrodes are an overflow basin. When the surface of the water is disturbed, some water will spill over from the pool. Real charges are like throwing a stone into the middle of the pool. The water will spill over as soon as the wave that has been created reaches the edge of pool, just like electrons excited by a laser pulse in the middle of the graphene,” explains Tobias Boolakee, lead author of the study and researcher at the Chair of Laser Physics.

“Virtual charges are like scooping the water from the edge of the pool without waiting for a wave to be formed. With electrons, this happens so quickly that it cannot be perceived, which is why it is known as a virtual charge. In this scenario, the laser pulse would be directed at the edge of the graphene right next to the gold electrodes.” Both virtual and real charges can be interpreted as binary logic (0 or 1).

Logic with lasers

The laser physicists at FAU have been able to demonstrate with their experiments for the first time that this method can be used to operate a logic gate – a key element in computer processors. The logic gate regulates how the incoming binary information (0 and 1) is processed. The gate requires two input signals, here electron waves from real and virtual charges, excited by two synchronized laser pulses. Depending on the direction and strength of the two waves, the resulting current pulse is either aggregated or erased. Once again, the electrical signal that the physicists measure can be interpreted as binary logic, 0 or 1.

“This is an excellent example of how basic research can lead to the development of new technology. Through fundamental theory and its connection with the experiments, we have uncovered the role of real and virtual charges which has opened the way to the creation of ultrafast logic gates,” says Ignacio Franco from the University of Rochester.

“It will probably take a very long time before this technology can be used on a computer chip. But at least we know that light wave electronics is a feasible technology,” adds Tobias Boolakee.

Reference: “Light-field control of real and virtual charge carriers” by Tobias Boolakee, Christian Heide, Antonio Garzón-Ramírez, Heiko B. Weber, Ignacio Franco and Peter Hommelhoff, 11 May 2022, Nature.
DOI: 10.1038/s41586-022-04565-9

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