Breaking the Speed ​​of Light: The Quantum Tunnel Mystery

In an amazing phenomenon of quantum physics known as tunneling, particles appear to move faster than the speed of light. However, physicists from Darmstadt believe that the time spent by particles in the tunnel has been measured incorrectly until now. They propose a new way to stop the speed of quantum particles.

In classical physics, there are strict rules that cannot be circumvented. For example, if a rolling ball does not have enough energy, it will not go over the hill, but will turn around before reaching the top and reverse direction. In quantum physics, this principle is not entirely strict: a particle can cross a barrier, even if it does not have enough energy to get through it. It behaves as if it is sliding through a tunnel, which is why this phenomenon is also known as “quantum tunneling.” What seems magical has concrete technical applications, for example in flash memory drives.

Quantum tunneling and relativity

In the past, experiments with faster-than-light particles have attracted some attention. After all, Einstein's theory of relativity prohibits speeds faster than light. The question is therefore whether the time required for tunneling has been properly “paused” in these experiments. Physicists Patrick Schach and Eno Giese from the University of Darmstadt follow a new approach to determining the “time” of a tunneling particle. They have now proposed a new way to measure this time. In their experiment, they measured it in a way that they believe is more suitable for the quantum nature of tunneling. They published their experiment design in the famous magazine Advancement of science.

Wave-particle duality and quantum tunneling

According to quantum physics, small particles such as atoms or particles of light have a dual nature.

Depending on the experiment, they behave like particles or like waves. Quantum tunneling highlights the wave nature of particles. A “wave packet” rolls toward the barrier, similar to water flow. Wave height indicates the probability of a particle materializing at that location if its position were measured. If a wave packet hits an energy barrier, part of it is reflected. However, a small portion penetrates the barrier, and there is a small possibility that the particle will appear on the other side of the barrier.

Re-evaluation of tunnel speed

Previous experiments observed that a light particle traveled a longer distance after tunneling than a particle that had a free path. Therefore, it would have traveled faster than light. However, researchers had to determine the particle's location after it passed. They chose the highest point in the wave packet.

“But the particle does not follow a path in the classical sense,” objects Eno Giese. It is impossible to determine exactly where a particle was at a given time. This makes it difficult to make statements about the time needed to get from A to B.

A new approach to measuring tunneling time

On the other hand, Shash Brief is guided by a quote from Albert Einstein: “Time is what you read on the clock.” They propose using the tunnel particle itself as a clock. The second unspent particle acts as a reference. By comparing these two natural clocks, it is possible to determine whether time passes more slowly, faster, or at the same speed during quantum tunneling.

The wave nature of particles facilitates this approach. The oscillation of waves is like the oscillation of a clock. Specifically, Schach and Giese propose using atoms as clocks. The energy levels of atoms oscillate at certain frequencies. After addressing A corn With a laser pulse, their levels initially oscillate synchronously – the atomic clock starts. During the tunnel, the rhythm changes slightly. A second laser pulse causes the two internal waves of the atom to overlap. Detecting interference makes it possible to measure how far apart two energy level waves are, which in turn is an accurate measurement of the elapsed time.

As for the second atom, which is not tunneled, it serves as a reference for measuring the time difference between digging tunnels and not digging tunnels. Physicists' calculations suggest that the tunnel particle will appear a little later. “The clock that was dug through the tunnel is a little older than the other clock,” says Patrick Schach. This seems to contradict experiments that attributed the speed of light to tunneling.

The challenge of implementing the experiment

In principle, the test could be done using current technology, Schach says, but it presents a huge challenge for experiments. This is because the time difference to be measured is only about 10^-26 Seconds – a very short time. The physicist explains that it helps to use clouds of atoms as clocks instead of individual atoms. It is also possible to amplify the effect, for example by artificially increasing clock frequencies.

“We are currently discussing this idea with our experimental colleagues, and we are in contact with our project partners,” Gizzi adds. It is very likely that the team will soon decide to conduct this exciting experiment.

Reference: “Unified theory of tunnel times promoted by Ramsey clocks” by Patrick Schach and Eno Giese, April 19, 2024, Advancement of science.
doi: 10.1126/sciadv.adl6078