What is time for quantum particles

What is "time" for quantum particles
by Robert Schreiber
Berlin, Germany (SPX) May 20, 2024

Physicists from Darmstadt propose a new method to measure the time it takes for particles to tunnel, challenging previous experiments that suggested particles could move faster than the speed of light. This phenomenon, known as quantum tunneling, allows particles to pass through barriers even if they don't have enough energy to go over them. This effect has practical applications, such as in flash memory drives.

In earlier experiments, particles appeared to tunnel faster than light, conflicting with Einstein's theory of relativity. Patrik Schach and Enno Giese from TU Darmstadt suggest a new approach to measure the tunneling time more accurately. They published their experimental design in "Science Advances."

Quantum particles, such as atoms or light particles, exhibit dual behavior, acting as both particles and waves. During quantum tunneling, a wave packet, representing the particle, hits an energy barrier. Part of the wave reflects, but a small portion penetrates the barrier, allowing the particle to appear on the other side.

Previous experiments measured the location of a tunneling particle by its wave packet's highest point. Enno Giese noted, "But the particle does not follow a path in the classical sense." This uncertainty makes it hard to determine the tunneling time.

Schach and Giese propose using the tunneling particle as a clock, comparing it with a non-tunneling reference particle. They suggest using atoms, which oscillate at specific frequencies, as clocks. By measuring the interference between two internal waves of the atom, the time elapsed during tunneling can be determined. A reference atom, which does not tunnel, allows for a comparison of the time difference.

Their calculations indicate that the tunneling particle shows a slightly delayed time. "The clock that is tunneled is slightly older than the other," said Patrik Schach. This finding contradicts earlier experiments that suggested superluminal speeds.

The proposed test can be conducted with current technology, though it presents challenges due to the extremely short time difference of around 10^-26 seconds. Using clouds of atoms instead of individual atoms and artificially increasing clock frequencies may help. Giese mentioned, "We are currently discussing this idea with experimental colleagues and are in contact with our project partners." An experimental team may soon attempt this experiment.

Research Report:A unified theory of tunneling times promoted by Ramsey clocks