Quantum tunnelling is an instantaneous process

An international team of scientists studying ultrafast physics has solved a mystery of quantum mechanics, finding that quantum tunnelling is an instantaneous process. Their research has been published in the journal Nature Physics.

At very small scales, quantum physics shows that particles such as electrons have wave-like properties - their exact position is not well defined. This means 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.

Australian National University (ANU) researchers Professor Kheifets and Dr Igor Ivanov are members of a team which studied ultrafast experiments at the attosecond scale (10^-18 seconds) - a timescale which had never been explored before. 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,” said Professor Kheifets. “But the mathematics says the time during tunnelling is imaginary - a complex number - which we realised meant it must be an instantaneous process.”

“A very interesting paradox arises, because electron velocity during tunnelling may become greater than the speed of light,” added Dr Ivanov. “However, this does not contradict the special theory of relativity, as the tunnelling velocity is also imaginary.”

The team’s calculations, which were made using the Raijin supercomputer, revealed that the delay in photoionisation originates not from quantum tunnelling but from the electric field of the nucleus attracting the escaping electron.

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

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

“We have modelled the most delicate processes of nature very accurately.”

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 areas such as electron microscopy, nuclear fusion and DNA mutations.

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