A long-standing quest for science and technology has been to create electronics and information processing that operate near the Ultrafast timescales allowed by the laws of nature. A promising approach to achieve this goal involves using laser light to guide the motion of electrons in matter, and then using this control to develop electronic circuit elements—a concept known as lightwave electronics.

Remarkably, lasers currently allow us to generate bursts of electricity on femtosecond timescales—that is, in a millionth of a billionth 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-Universität Erlangen-Nürnberg (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. The feat, reported on May 11 in the journal Nature, was accomplished by harnessing and independently controlling form the first time, the real and virtual charge carriers that compose these ultrafast bursts of electricity. The researchers’ advances have opened the door to information processing at the petahertz limit, where one quadrillion computational operations can be processed per second. That is almost a million times faster than today’s computers operating with gigahertz clock rates, where 1 petahertz is 1 million gigahertz.

“This is a great example of how fundamental science can lead to new technologies,” says Ignacio Franco, an associate professor of chemistry and physics at Rochester who, in collaboration with doctoral student Antonio José Garzón-Ramírez ’21 (PhD), performed the theoretical studies that lead to this discovery.

In recent years, scientists have learned how to exploit laser pulses that last a few femtoseconds to generate ultrafast bursts of electrical currents. This is done, for example, by illuminating tiny graphene-based wires connecting two gold metals. The ultrashort laser pulse sets in motion, or “excites,” the electrons in graphene and, importantly, sends them in a particular direction—thus generating a net electrical current. Laser pulses can produce electricity far faster than any traditional method—and do so in the absence of applied voltage. Further, the direction and magnitude of the current can be controlled simply by varying the shape of the laser pulse (that is, by changing its phase).

The research groups of Franco and of FAU’s Peter Hommelhoff have been working for several years to turn light waves into ultrafast current pulses. In trying to reconcile the experimental measurements at Erlangen with computational simulations at Rochester, the team had a realization: In gold-graphene-gold junctions, it is possible to generate two flavors—“real” and “virtual”—of the particles carrying the charges that compose these bursts of electricity.

Strikingly, the team discovered that by changing the shape of the laser pulse, they could generate currents where only the real or the virtual charge carriers play a role. In other words, they not only generated two flavors of currents, but they also learned how to control them independently, a finding that drastically augments the elements of design in lightwave electronics.

Using this augmented control landscape, the team was able to experimentally demonstrate, for the first time, logic gates that operate on a femtosecond timescale. Logic gates are the basic building blocks needed for computations. They control how incoming information, which takes the form of 0 or 1 (known as bits), is processed. Logic gates require two input signals and yield a logic output.

In the researchers’ experiment, the input signals are the shape or phase of two synchronized laser pulses, each one chosen to only generate a burst of real or virtual charge carriers. Depending on the laser phases used, these two contributions to the currents can either add up or cancel out. The net electrical signal can be assigned logical information 0 or 1, yielding an ultrafast logic gate. “It will probably be a very long time before this technique can be used in a computer chip, but at least we now know that lightwave electronics is practically possible,” says Tobias Boolakee, who led the experimental efforts as a PhD student at FAU.

Source: This news is originally published by scitechdaily

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