New research into quantum mechanics has confirmed an effect known as "quantum tunneling" involved in real-life phenomena like fusion reactions and radioactive decay, European researchers say.

Quantum tunneling is the effect of quantum particles moving through an energy state considered impossible in the context of what are considered classical mechanics.

Under classical physics theory, objects can only move from one place to another if they possess sufficient energy for the shift. For example, a ball arriving slowly at the base of a hill may have insufficient velocity to roll over the hill without some energy given to it from an external source.

However, quantum particles don't behave like a classical object; they don't have a fixed location in space until a measurement of them is made. Until then, they have the attribute of existing in every possible location, so could suddenly be on the opposite side of the hill without requiring an external nudge.

In the example of the ball, it means it could suddenly be on the opposite side of the hill, by tunneling through, not over the hill.

While the ball is made up of too many particles and the hill of too many layers for any likelihood of that happening, while that likelihood is very small, it is not zero. Researchers at the Institute for Experimental Physics of the University of Innsbruck, Austria, say.

A fundamental hypothesis of the tunnel effect involves one single particle penetrating one single barrier, but the Austrian researchers in their experiment report quantum particles moving through a series of as many as  five potential barriers under circumstances where a single particle would not successfully make the move.

Several particles apparently assisted each other in penetrating the multiple barriers though strong interactions with each other, study co-author Hanns-Christoph Nagerl says.

Writing in the journal Science, the researchers described how they caused atoms in a cloud of Cesium gas cooled to close to absolute zero -- to minimize their energy level -- to successfully tunnel through the multiple layers.

An individual atom's tunneling energy might only allow it to penetrate a single barrier, but in a frictionless environment that energy gets recycles in a phenomenon known as "Bose enhancement" that helps other particles move along through subsequent barriers, they found.

Thus, having other particles in the way is a help, not a hindrance, as the interactions suggest that under certain conditions long-range tunneling by multiple particles is possible, the researchers said.