Scientists now know how fast electronics could theoretically get. While computers and smartphones are getting faster, there are many limits to how much faster they can get – this is due to the properties of the materials, but also the very laws of physics.

To investigate the latter, a team from TU Wien (Vienna), TU Graz, and the Max Planck Institute of Quantum Optics created a very special setup, using lasers and non-conducting materials. This scenario, while not being an architecture for current electronics, gave scientists a way to test quantum mechanics to its limit.

And there is a limit. According to the work, published in Nature Communications, controlled processes involving light and electronics in materials cannot exceed one petahertz. That’s about 1,000 trillion processes per second. Commercially available processors have a clock frequency of the order of 4.5 gigahertz, so the limit is over 250,000 times faster.

"For a long time, such processes were considered instantaneous," co-author Prof. Christoph Lemell from TU Wien, said in a statement. "Today, however, we have the necessary technology to study the time evolution of these ultrafast processes in detail."

The limit comes from one of the cornerstones of quantum mechanics: the uncertainty principle. You might be familiar with it described as: the more precisely you know the position of a particle, the less precisely its momentum can be predicted, and vice versa. This can also be applied to energy and time. So for faster speed, you need shorter laser pulses, which means the energy is not precisely defined.

And energy is key. For electricity to flow, you need free electrons, and the energy provided to the system can separate the electrons from the atoms. So if there is uncertainty on the energy you deliver, your system might not work as you expect beyond a certain threshold of short-time pulses.

"We can tell exactly at which point in time the free charge carriers are created, but not in which energy state they are," explained Lemell. "Solids have different energy bands, and with short laser pulses many of them are inevitably populated by free charge carriers at the same time."

While the petahertz is a nice round limit, the team believes that it is unlikely that electronics are going to get near it. There are other physical properties related to the specific materials and the specific setup that ought to be tested to understand the actual physical speed limit. But at least there are now approaches that can reach those limits.