An atom consists of protons, neutrons, electrons, and a nucleus. Protons and neutrons are in the center of the atom, making up the nucleus. On the other hand, electrons revolve around the nucleus in orbits. But what is in between the nucleus and the electron?
Plenty of space is available between electron orbits in the nucleus so that a giant atom can take place with ordinary atoms. All these atoms shape a powerless bond, making another exotic state of matter at cool temperatures, also known as “Rydberg polarons”.
Now, scientists at the TU Wien, Harvard University, and Rice University have explored his state of matter. They have presented their work in the journal Physical Review Letters.
Two different fields of atomic physics can be studied in extreme conditions only. Those fields are Bose-Einstein condensates and Rydberg atoms. A Bose-Einstein condensate is a state of matter created by atoms at ultracold temperatures close to absolute zero. Rydberg atoms are atoms in which one single electron is lifted into a highly excited state and orbits the nucleus at a considerable distance.
Initially, a Bose-Einstein condensate was made with strontium iotas. With the help of a laser, energy was exchanged to one of these atoms, transforming it into a Rydberg atom with a large atomic radius.
The radius of the orbit on which the electron revolves is substantially bigger than the average distance between two atoms in the condensate. In this manner, the electron not only orbits its own atomic nucleus, but various different atoms lie inside its orbit.
Relying on the radius of the Rydberg molecule and the density of the Bose-Einstein condensate, upwards of 170 extra strontium atoms might be encased by the huge electronic orbit. Such atoms rarely influence this Rydberg electron’s path.
Prof. Shuhei Yoshida said, “The atoms do not carry any electric charge therefore they only exert a minimal force on the electron. But to a minimal degree, the electron still feels the presence of the neutral atoms along its path. It is scattered at the neutral atoms, but only very slightly, without ever leaving its orbit. The quantum physics of slow electrons permits this kind of scattering, which does not transfer the electron into a different state.”
“As computer simulations show, this comparatively weak kind of interaction decreases the system’s total energy, and so a bond between the Rydberg atom and the other atoms inside the electronic orbit is created. It is a highly unusual situation.”
“Normally, we are dealing with charged nuclei, binding electrons around them. Here, we have electron-binding neutral atoms. However, the bond is much weaker than the bond between atoms in a crystal. Therefore, this exotic state of matter, called Rydberg polarons, can only be detected at very low temperatures. If the particles were moving any faster, the bond would break.”
Professor Joachim Burgdörfer at TU Wien said, “This new, weakly bound state of matter is an exciting new possibility of investigating the physics of ultracold atoms. That way, one can probe the properties of a Bose-Einstein condensate on very small scales with very high precision.”