Lab creates strange trilobite-shaped molecule for first time

For the first time, physicists have successfully created a strange, fragile structure called a trilobite Rydberg molecule in the laboratory.

Constructing and observing these strange atomic structures gave scientists new insights into the quantum behavior of electrons as they scatter near atoms.

Because their chemical bonds are unlike any other we know of, these findings open the way to developing better theoretical models of molecules and understanding their dynamics.

Rydberg molecules are created from a type of atom called a Rydberg atom. In a normal atom, there is a nucleus surrounded by tiny groups of electrons. If you add a little energy to an atom, the electron population expands a little, making the atom larger and looser.

When you add a lot of energy under conditions that allow it to still retain electrons, you get a Rydberg atom. For an atom, it expands quite a bit, a few microns in diameter, and the electrons are bound as loosely as possible so they don’t fly away.

Because they are so loose, the behavior of Rydberg atoms is somewhat exaggerated, which makes them very useful for conducting experiments.

Molecules are arrangements of atoms that are held together in some way, such as by common electrons or perhaps by contrasting charges. If you use Rydberg atoms, you get Rydberg molecules, but the way the atoms stick to each other can be very different from the bonds that connect more traditional molecules.

They can look very different, and their distribution electron patterns may resemble those of a trilobite or a butterfly.

A team of scientists from Herwig Ott’s laboratory, led by Max Althn, a physicist at the University of Kaiserslautern-Landau, created pure trilobite Rydberg molecules for the first time.

They started with rubidium atoms and supercooled them to just 0.0001 degrees above absolute zero. They then used lasers to excite some atoms into the Rydberg state.

“During this process, the outermost electrons are in each case carried into distant orbits around the atomic body,” Ott said. “The orbital radius of electrons can exceed one micron, making the electron cloud larger than a small bacterium.”

Rydberg molecules can be created by bringing a ground-state atom that is not excited into a Rydberg state into the Rydberg atom’s fluffy electron population. The two atoms are held together not by a standard chemical bond but by strange quantum attraction. Together.

“Quantum mechanical scattering of the Rydberg electrons in the ground-state atom sticks the two together,” explains Alson.

“Imagine an electron spinning rapidly around the nucleus. On each round trip, it collides with a ground-state atom. Counterintuitively, quantum mechanics tells us that these collisions result in an effective attraction between the electron and the ground-state atom.”

As a result of repeated collisions, the electrons are distributed into interference patterns that resemble the segmented carapace of a trilobite.

It also has some other fascinating and strange properties. The length of a molecular bond is almost the same size as the Rydberg orbital, that is, quite large for the atomic scale. And the attraction between electrons and ground-state atoms is also quite high.

This means that Rydberg molecules have a higher electric dipole moment than any other molecule; that is, the separation between positive and negative charges, also called polarity.

The electric dipole moment of the trilobite Rydberg molecules observed by Althn and his colleagues is over 1,700 debyes, which is very high. For water molecules, this measurement is less than 2 Debye.

The ability to not only create but detect pure trilobite Rydberg molecules gives physicists new tools to test and understand the quantum realm.

It also has potential applications in quantum information processing. The researchers say it could be used more broadly to study these strange molecules in different species.

“In summary, we have measured two vibrational series of pure trilobite Rydberg molecules by employing three-photon photoassociation,” they wrote. “By this method, three Leafworm molecules should be possible.”

The study was published in nature communications.