Scientists solve quantum tunnelling mystery

An international team of scientists studying ultrafast physics has solved a mystery of quantum mechanics and found that quantum tunnelling is an instantaneous process, the Australian National University said on Thursday.

The new theory could lead to faster and smaller electronic components for which quantum tunnelling is a significant factor. It will also lead to a better understanding of diverse areas such as electron microscopy, nuclear fusion and DNA mutations.

"Timescales this short have never been explored before. It's an entirely new world," Xinhua news agency quoted Anatoli Kheifets from The Australian National University (ANU), who is a member of the international team, as saying in a press statement.

At very small scales, quantum physics shows that particles such as electrons have wave-like properties and their exact position is not well defined, meaning that they can occasionally sneak through apparently impenetrable barriers, a phenomenon called quantum tunnelling.

Quantum tunnelling plays a role in a number of phenomena, such as nuclear fusion in the sun, scanning tunnelling microscopy and flash memory for computers. However, the leakage of particles also limits the miniaturisation of electronic components.

Kheifets and Igor Ivanov, from the ANU Research School of Physics and Engineering, are members of a team which studied ultrafast experiments at the attosecond scale (one quintillionth of a second) -- a field that has developed in the past 15 years.

Until their work, a number of attosecond phenomena could not be adequately explained, such as the time delay when a photon ionised an atom.

"At that timescale, the time an electron takes to quantum tunnel out of an atom was thought to be significant. But the mathematics says the time during tunnelling is imaginary, a complex number, which we realised meant it must be an instantaneous process," said Kheifets.

"A very interesting paradox arises, because electron velocity during tunnelling may become greater than the speed of light. However, this does not contradict the special theory of relativity, as the tunnelling velocity is also imaginary," said Ivanov, who has taken up a position at the Centre for Relativistic Laser Science in South Korea.

The team's calculations made using the Raijin supercomputer showed that the delay in photoionisation originates not from quantum tunnelling but from the electric field of the nucleus attracting the escaping electron.

The results provide an accurate calibration for future attosecond-scale research, said Kheifets.

"It's a good reference point for future experiments, such as studying proteins unfolding, or speeding up electrons in microchips," he said.

The research is published in the Nature Physics journal.