Laser pulses for ultra-fast signal processing could make computers a million times faster

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

Simulating complex scientific models on the computer or processing large volumes of data, such as editing video material, requires considerable computing power and time. Researchers from the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) Chair of Laser Physics and a team from the University of Rochester in New York demonstrated how the speed of fundamental computing operations could be increased at the future up to a million times faster using laser pulses. Their findings were published on May 11, 2022 in the journal Nature.

The computing speed of today’s computer and smartphone processors is given by field-effect transistors. In the competition to produce faster devices, these transistors are constantly being reduced in size to fit as many of them as possible on chips. Modern computers already operate at the blazing speed of several gigahertz, which translates to several billion computational operations per second. The latest transistors measure only 5 nanometers (0.000005 millimeters), the equivalent of little more than a few atoms. There are limits to what chipmakers can do and at some point it will no longer be possible to downsize transistors.

Light is faster

Physicists work hard to control electronics with light waves. The oscillation of a light wave takes about a femtosecond, or a millionth of a billionth of a second. Controlling electrical signals with light could make the computers of the future more than a million times faster, which is the goal of petahertz signal processing or light wave electronics.

From light waves to current pulses

The electronics are designed to transfer and process signals and data as logical information, using binary logic (1s and 0s). These signals can also take the form of current pulses.

Researchers from the Chair of Laser Physics have studied how light waves can be converted into current pulses to several years. In their experiments, the researchers shed light on a structure of graphene and gold electrodes with ultrashort laser pulses. The laser pulses induce electronic waves in the graphene, which travel to the gold electrodes where they are measured as current pulses and can be processed as information.

Real and virtual loads

Depending on where the laser pulse hits the surface, the electron waves propagate differently. This creates two types of current pulses called real and virtual loads.

Tobias Boolakee

Tobias Boolakee. Credit: FAU/Johanna Hojer

“Imagine that graphene is a swimming pool and the gold electrodes are an overflow pool. When the water surface is disturbed, water will overflow from the pool. The actual charges are like throwing a stone in the middle of The water will overflow as soon as the wave that has been created reaches the edge of the 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 picking up water from the edge of the swimming pool without waiting for a wave to form. With electrons, it happens so quickly that it cannot be perceived, which is why it is called a charge In this scenario, the laser pulse would be directed at the edge of the graphene right next to the gold electrodes.The virtual and real charges can be interpreted as binary logic (0 or 1).

Logic with lasers

The FAU laser physicists were able to demonstrate for the first time with their experiments that this method can be used to operate a logic gate – a key component of computer processors. The logic gate regulates how incoming binary information (0 and 1) is processed. The gate requires two input signals, here electronic waves from real and virtual loads, 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. Again, the electrical signal that physicists measure can be interpreted as a logical binary, 0 or 1.

“This is an excellent example of how fundamental research can lead to the development of new technologies. Thanks to the fundamental theory and its connection with experiments, we discovered the role of real and virtual charges which paved the way for the creation of ultrafast logic gates”, explains Ignacio Franco from the University of Rochester.

“It will probably be a long time before this technology can be used on a computer chip. But at least we know that lightwave 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, May 11, 2022, Nature.
DOI: 10.1038/s41586-022-04565-9

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