Scientists discover a new "speed limit" for all electronic devices

Putting the laws of quantum mechanics to the test.
Chris Young
Concept of digital technology.nadla/iStock

It's difficult to imagine a society that's reached the ceiling of innovation for electronic devices — the number of as-yet-unknown implications is overwhelming.

But now, thanks to a global team of researchers, we may at least have a fleeting idea of what's to come.

The researchers, from TU Wien, TU Graz, and the Max Planck Institute of Quantum Optics, calculated the ultimate speed limit for electronic devices, the point at which the laws of quantum mechanics prevent microchips from becoming any faster, according to a study published in Nature Communications.

The fastest devices in the world are known as optoelectronics — systems that use light to control electricity. The new study outlines the limit for optoelectronics by calculating the speed at which the most powerful examples of these devices can operate.

For their calculations, the researchers experimented with semiconductor materials and lasers. They used a quick laser pulse to energize electrons in the material before a second, slightly longer laser pulse was emitted to produce an electrical current in the material.

The team observed the current while applying shorter and shorter laser pulses until Heisenberg's uncertainty principle allowed them to go no further — the principle states that the more accurately you measure one variable of a particle, such as its position, the more uncertain other variables, such as momentum will be, and vice versa. The scientists also applied their findings to complex computer simulations to make better sense of their observations.

The upper limit of optoelectronics

Using shorter laser pulses meant the researchers could calculate exactly when the electrons gained energy. But, due to Heisenberg's principle, this came at the cost of reduced certainty over the amount of energy gained. That would likely be an insurmountable hurdle for electronic devices, which require exact calculations of electrons to be controlled precisely.

So, according to the researchers, the upper limit of optoelectronic systems is one Petahertz, which is equivalent to a million Gigahertz. To go any faster would be to break the laws of quantum physics.

The team does also state that many other technical hurdles would stand in the way of getting anywhere near that speed, so we're not about to see optoelectronic devices that come anywhere near that upper limit.

"Realistic technical upper limits are most likely considerably lower," the scientists say in a press release. "Even though the laws of nature determining the ultimate speed limits of optoelectronics cannot be outsmarted, they can now be analyzed and understood with sophisticated new methods." Knowing the ceiling allows researchers and developers to better understand the constraints they're working with and adjust their work accordingly.

Abstract:

Light-field driven charge motion links semiconductor technology to electric fields with attosecond temporal control. Motivated by ultimate-speed electron-based signal processing, strong-field excitation has been identified viable for the ultrafast manipulation of a solid’s electronic properties but found to evoke perplexing post-excitation dynamics. Here, we report on single-photon-populating the conduction band of a wide-gap dielectric within approximately one femtosecond. We control the subsequent Bloch wavepacket motion with the electric field of visible light. The resulting current allows sampling optical fields and tracking charge motion driven by optical signals. Our approach utilizes a large fraction of the conduction-band bandwidth to maximize operating speed. We identify population transfer to adjacent bands and the associated group velocity inversion as the mechanism ultimately limiting how fast electric currents can be controlled in solids. Our results imply a fundamental limit for classical signal processing and suggest the feasibility of solid-state optoelectronics up to 1 PHz frequency.

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