Australasian Science: Australia's authority on science since 1938

Quantum Tunnelling in an Instant

The discovery that quantum tunnelling is an instantaneous process could lead to faster and smaller electronic components and a better understanding of electron microscopy, nuclear fusion and DNA mutations.

“We have modelled the most delicate processes of nature very accurately,” says Prof Anatoli Kheifets of The Australian National University. “Time scales this short have never been explored before.”

Particles such as electrons have wave-like properties, and their exact position is not well defined. This means they can occasionally “tunnel” through apparently impenetrable barriers.

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 ANU colleague Dr Igor Ivanov were part of an international team that studied ultrafast experiments at the attosecond scale (10-18 seconds). “At that timescale the time an electron takes to quantum tunnel out of an atom was thought to be significant,” Kheifets says. “But the mathematics says the time during tunnelling is imaginary – a complex number – which we realised meant it must be an instantaneous process.”

Ivanov explains that “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.”

The team’s calculations, which were published in Nature Physics, 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. “It’s a good reference point for future experiments, such as studying proteins unfolding or speeding up electrons in microchips,” Kheifets says.