Scientists play 'table tennis' with two atoms and a light particle

In an important breakthrough, scientists have persuaded two atoms to play a simple game of table tennis, bouncing a light particle back and forth.

But this extremely tiny 'game' where the atoms pass the light particle – known as a photon – between each other is a significant moment in quantum physics, and could have important uses in communication.

The research was simulated, as it's currently impossible to measure events this tiny. It relied on a phenomenon similar to a whispering gallery, where people can hear each other clearly despite being far apart, with the photon channelled perfectly from one atom to the other, and back again.

Prof Stefan Rotter, from the Institute of Theoretical Physics at TU Wien in Vienna, said the achievement was particularly important thanks to the fact that light particles are both particles and waves at the same time. He said: "If an atom emits a photon somewhere in free space, the direction of emission is completely random. This makes it practically impossible to get another distant atom to catch this photon again.

"The photon propagates as a wave, which means that nobody can say exactly in which direction it is travelling. It is, therefore, pure chance whether the light particle is reabsorbed by a second atom or not."

How did the researchers do it?

Normally, photon are emitted in a random direction, but the researchers used a lens to channel the tiny particles on the right route in their simulation.

The research team, therefore, came up with a better strategy based on the concept of the fish-eye lens, which was developed by James Clerk Maxwell, the founder of classical electrodynamics. The lens comprises a spatially varying refractive index – light rays are bent in a Maxwell fish-eye lens.

Researcher Oliver Diekmann said: "In this way, it is possible to ensure that all rays emanating from one atom reach the lens's edge on a curved path, are subsequently reflected, and then arrive at the target atom on another curved path."

Professor Rotter added: "We were able to show that the coupling between the atom and these different oscillating modes can be adapted in such a way that the photon is transferred from one atom to the other one almost certainly – quite different from what would be the case in free space."

Why does it matter?

The research could be useful in communications and help to further our understanding of quantum physics, the scientists said.

The effect has been demonstrated theoretically, but practical tests are possible with today's technology. "In practice, the efficiency could be increased even further by using not just two atoms, but two groups of atoms," Rotter said. "The concept could be an interesting starting point for quantum control systems to study effects at extremely strong light-matter interaction."

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