A hidden limit of space and time could unlock electronics 100,000 times faster

- Date:

- November 7, 2026

- Source:

- University of Regensburg

- Summary:

- Scientists have discovered a surprising quantum limit that prevents electrons from being tracked with unlimited precision in both space and time. The breakthrough could pave the way for manipulating chemical reactions and developing electronics hundreds of thousands of times faster than today's technology.

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Quantum physics places fundamental limits on what scientists can know about the behavior of particles. Werner Heisenberg's famous uncertainty principle states that certain properties, such as a particle's position and momentum, cannot both be measured with unlimited precision. This restriction is not caused by flaws in scientific instruments. It is built into the laws of nature.

But position and time are different. Heisenberg's uncertainty principle does not impose the same restriction on these quantities. Now, researchers have experimentally demonstrated another fundamental limitation: an electron's location and its behavior over time cannot both be determined with arbitrary precision. Known as the "space-time limit," this newly observed relationship could have major implications for the future of quantum technology and ultrafast electronics.

The discovery comes from an international collaboration involving research groups at the Regensburg Center for Ultrafast Nanoscopy (RUN), led by Profs. Jascha Repp, Rupert Huber, Franz Giessibl, and Klaus Richter, along with a team at the Max Planck Institute in Hamburg led by Angel Rubio.

Watching Electrons Move at Incredible Speeds

Understanding how matter behaves at the smallest scales is essential for developing the next generation of technology. Advances in clean energy, quantum computing, and powerful electronics for artificial intelligence all depend on knowing how chemical reactions unfold, how light interacts with materials, and how electrons travel through electronic devices.

However, even the sharpest microscopic photographs cannot reveal the full picture. Scientists also need to observe how these processes change over time, effectively creating slow-motion movies of events occurring at the atomic scale.

At RUN, researchers are developing ultrafast microscopes capable of recording the movements of electrons, atoms, and molecules with extraordinary precision in both space and time. About ten years ago, scientists in Regensburg used ultrafast scanning tunneling microscopy to resolve the movement of a single molecule across space and time for the first time.

Tracking individual electrons presents an even greater challenge. At these microscopic distances, electrons can move roughly a thousand times faster than atoms and molecules, with important changes taking place over just attoseconds.

To appreciate how extreme these scales are, consider that an atom is approximately ten million times smaller than a millimeter. An attosecond is one-billionth of a billionth of a second. The difference between an attosecond and a second is comparable to the difference between one second and the entire age of the universe.

Making these measurements is especially difficult because electrons do not behave like ordinary objects. Their motion follows the unusual laws of quantum mechanics rather than the familiar rules of classical physics.

Ultrafast Lasers Reveal Quantum Tunneling

To observe electron behavior at these extraordinary speeds, the researchers built a new laser system that provides much finer time resolution than earlier experiments. The system allows them to control and study the quantum motion of individual electrons directly.

In the experiments, carefully timed laser pulses drive electrons from an extremely sharp metal tip toward a silver surface. The distance they travel is only a few atomic diameters.

The researchers detect this movement by measuring the resulting electrical current. To determine exactly when the electrons move, they use two pulses of light separated by a precisely controlled interval.

Simon Maier, the lead author of the paper, explains: "By varying the time interval between the two laser pulses, we can directly observe how the electrons respond."

This approach revealed clear evidence of electron motion occurring on attosecond timescales. It showed that the laser pulses could transfer electrons within these incredibly brief intervals while allowing scientists to observe the process as it happened.

What makes the result particularly remarkable is how the electrons travel. Instead of moving like conventional particles, they behave as quantum waves. This allows them to pass through an energy barrier separating the metal tip from the silver surface, even though classical physics predicts they should not have enough energy to cross it.

This phenomenon, known as quantum tunneling, is somewhat like an object passing through a solid wall without breaking or damaging it.

"Our measurement can be understood as a high-speed camera for the electron wave packets, since you can see at what point in time the tunneling process takes place," explains Katharina Glöckl, a doctoral student and co-author of the publication.

A Surprising 500-Attosecond Delay

To understand the measurements more deeply, researchers working with Prof. Angel Rubio performed sophisticated quantum simulations of the electrons' behavior near the "space-time limit."

Their calculations closely reproduced the experimental findings and uncovered another remarkable detail. The electrons did not respond to the light field instantaneously. Instead, their motion lagged behind it by approximately 500 attoseconds.

At such extreme scales, several fundamental features of quantum physics become important simultaneously.

For example, the researchers found that the laser pulses could not be described entirely by treating light as a wave or entirely by treating it as individual particles called photons. Their effects displayed characteristics of both descriptions. This combination was essential for exploring electron behavior so close to the "space-time limit."

The team also discovered that controlling electron motion over extremely short intervals changes how the electrons are distributed in space. Quantum mechanics describes these electrons using wave packets, which represent how their wave properties extend across different locations.

The relationship between the timing of electron motion and the spatial extent of these wave packets revealed the central limitation behind the discovery.

A Hidden Tradeoff Between Space and Time

Raffael Spachtholz, another co-author of the study, explains: "The more precisely we want to pin down the electron's position in time, the more energy we need to provide. And as a result, the electron wave packet spreads out more spatially."

In other words, improving the precision of an electron's timing comes with a cost. The more tightly researchers define when its motion occurs, the more broadly its quantum wave packet spreads through space.

To examine this relationship experimentally, the team placed a single atom on the surface to confine the electron wave packets to an extremely small region immediately before the laser pulses arrived.

This setup allowed the scientists to directly measure the connection between the electrons' spatial distribution and the timing of their motion.

Importantly, even when the electrons received substantial energy from the laser pulses, their wave packets remained sufficiently localized for microscopy with atomic spatial resolution and attosecond time resolution.

The findings provide experimental insight into a fundamental space-time constraint that scientists had previously only suspected. They also make it possible to systematically investigate how changes in electron motion over time affect the spatial structure of quantum wave functions.

Could Quantum Electronics Become Hundreds of Thousands of Times Faster?

Beyond revealing a new aspect of quantum behavior, the discovery could open the door to technologies that operate on timescales far beyond the capabilities of today's electronics.

One especially promising possibility involves using precisely controlled electron wave packets to influence chemical reactions.

Transferring a single electron to a molecule represents the smallest possible transfer of electric charge. But when that electron is concentrated within an exceptionally small region of space and time, the resulting local peak current density can reach as much as 1 trillion amperes per square centimeter.

Such extreme conditions could give scientists new ways to control chemical bonds and observe how molecules change during reactions.

"In the future, we want to use such wave packets to specifically trigger chemical reactions and observe, on the relevant length and time scales, how chemical bonds can be broken or altered," explains Prof. Jascha Repp enthusiastically.

The implications could extend well beyond chemistry. Greater control over electron motion may eventually help engineers develop electronic devices and quantum information systems that operate at speeds approaching the fundamental limits of electron dynamics.

"In the long term, the insights gained could also contribute to operating electronics and quantum information processing at the intrinsic speed limit of electron motion itself -- hundreds of thousands of times faster than the currently dominant CMOS technology," adds Prof. Rupert Huber.

That possibility remains a long term technological goal rather than an achievement demonstrated in the current experiments. Nevertheless, the findings provide a new foundation for exploring how electrons can be manipulated at the smallest distances and shortest timescales.

For Repp and Huber, the results suggest that the range of potential applications is extraordinarily broad. They believe that future advances in controlling electrons at the space-time limit may ultimately depend more on human creativity than on the constraints imposed by nature.

Story Source:

Materials provided by University of Regensburg. Original written by Karoline Stürmer. Note: Content may be edited for style and length.

Journal Reference:

- S. Maier, R. Spachtholz, K. Glöckl, C. M. Bustamante, S. Lingl, M. Maczejka, J. Schön, A. Riedel, K. Richter, F. J. Giessibl, F. P. Bonafé, M. A. Huber, A. Rubio, J. Repp, R. Huber. Tracking electrons at the space-time limit. Nature Photonics, 2026; 20 (8): 961 DOI: 10.1038/s41566-026-01932-0

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