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Monday Oct 03, 2022

Ultrafast Computers are Coming: Laser Bursts Drive the Fastest-Ever Logic Gates

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 direction and magnitude by simply changing the phase of the laser pulse, which allows you to change the shape of the light.

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 at 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 linked to gold so both real and imaginary charge carriers are absorbed into the metal to create a net current.

The team found that they could create currents by altering the shape of the laser pulse. This was a remarkable discovery. They were able to generate two types of currents and also learn how to control them separately, which is a significant improvement in lightwave electronics design elements.

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