The orbit of an electron (blue) around a nucleus (red) was increased, allowing other atoms (green) inside. Tu Wien

A team of scientists has described how a new state of matter can be created, by essentially putting atoms inside other atoms.

Published in the journal Physical Review Letters, the work comes from the Vienna University of Technology (TU Wien) in Austria, Harvard University in Massachusetts, and Rice University in Texas.

This state of matter is referred to as “Rydberg polarons”. It basically involves making use of the space between the electron and the nucleus inside an atom, enough to fit other atoms inside.

“The average distance between the electron and its nucleus can be as large as several hundred nanometres – that is more than a thousand times the radius of a hydrogen atom”, said Professor Joachim Burgdörfer from the University of Vienna, a co-author on the paper, in a statement.

To make their finding, the team created what’s called a Bose-Einstein condensate with strontium atoms. This is a state of matter in which atoms are cooled to almost absolute zero, giving rise to some unusual quantum properties. Not least, they tend to share quantum states.

The team then transferred energy to one of the atoms using a laser, which kicked out one of its electrons into a much wider “orbit” and vastly increase its atomic radius, turning it into a Rydberg atom.

As a result, up to 170 other strontium atoms could be enclosed within the orbit of the outer electron – although note it’s less an orbit, and more a “cloud of probability” as to where the electron might be, as Science Alert pointed out.

The presence of the other atoms exerts a minimal force on the electron, causing it to be scattered very slightly. This creates a weak bond between the overall Rydberg atom and the other atoms, leading to an exotic state of matter – a Rydberg polaron.

It can only be detected at extremely low temperatures, but it could allow for some rather exciting physics in the future. It’s the first time Rydberg polarons have been observed – previously, we’ve only seen Rydberg molecules, in which the distant electron binds the atom to another atom.

“For us, this new, weakly bound state of matter is an exciting new possibility of investigating the physics of ultracold atoms”, Burgdörfer added. “That way one can probe the properties of a Bose-Einstein condensate on very small scales with very high precision.”

In their paper, the researchers said there were a number of avenues still to be explored by this research, including working out how polarons interact with each other. For now, however, it’s a major breakthrough in subatomic physics.