Listening to the atom group chat

Dutch and German researchers have intercepted a “chat” between two atoms, which may have interesting implications for research into quantum computing.

Atoms don’t actually talk, but they do interact via a property called spin.

“These spins influence each other, like compass needles do when you bring them close together,” explains team leader Sander Otte from the Delft University of Technology (TU Delft) in the Netherlands.

“If you give one of them a push, they will start moving together in a very specific way. But according to the laws of quantum mechanics, each spin can be simultaneously point in various directions, forming a superposition. This means that actual transfer of quantum information takes place between the atoms, like some sort of conversation.”

In a paper published in Science, Otte and fellow researchers used a scanning tunnelling microscope to place two titanium atoms very close to each other – just one millionth of a millimetre apart. Then, they set one atom spinning to see what the other would do.

But the traditional technique to do this – spin resonance, which uses precise radio signals to twist the atom – would have been too slow to make the desired observations.

“You have barely started twisting the one spin before the other starts to rotate along,” says lead author Lukas Veldman, also from TU Delft. “This way you can never investigate what happens upon placing the two spins in opposite directions.”

Instead, they used a burst of electric current to smash electrons into one atom and reverse its spin, which resulted in a quantum interaction.

“We always assumed that during this process, the delicate quantum information – the so-called coherence – was lost,” explains Otte, with chaos from the electrons transferring to the spin.

But the results suggest that any random electron could initiate coherent superposition and allow the exchange of information.

“Crucially for this to happen is that both spins become entangled: a peculiar quantum state in which they share more information about each other than classically possible,” says Markus Ternes, co-author from the RWTH Aachen University and the Research Center Jülich.

The research could have applications for quantum computers, which encode information in qubits – not only able to represent a 0 or 1 but also achieve a mixed state of coherent superposition, which is key to quantum computing’s power.

The next stage is to look at the chatter between even more atoms.

“Here we used two atoms, but what happens when you use three? Or ten, or a thousand?” asks Veldman. “Nobody can predict that, as computing power falls short for such numbers. Perhaps one day we will be able to listen to quantum conversations that nobody could ever hear before.”

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