Rydberg atoms are giant, excited atoms in which an electron travels far away from the nucleus. Scientists now believe these atoms can form molecules so huge that a virus could fit completely inside - and exist in two configurations simultaneously!
These hypothetical Rydberg molecules are the product of a fairly convincing thought experiment by Seth Rittenhouse and Hossein Sadeghpour of the Harvard-Smithsonian Center for Astrophysics. They imagined a rubidium atom in an excited, Rydberg state and a regular, much smaller molecule made up of rubidium and potassium. This second molecule would have a positive electrical charge on one end and a negative one on the other.
If the wandering electron of the Rydberg rubidium came in contact with the positively charged end of the rubidium-potassium molecule, the attraction wouldn't be quite strong enough to rip the electron away from its parent atom. Rather, the atom and the molecule would bond together, forming what Rittenhouse and Sadeghpour have dubbed a Rydberg molecule. The predicted bond between these two would be unlike any other bond ever seen in chemistry.
But it gets weirder. The pair predict that this Rydberg molecule would demonstrate the quantum property known as superposition, in which an object is quite literally in two places (or configurations) at once. In this instance, the potassium-rubidium molecule would actually point in two different directions simultaneously, a property that has been nicknamed the "Rydberg cat" after Erwin Schrodinger's legendary feline.
Rittenhouse thinks this fact could be exploited to put Rydberg molecules to work as qubits, the bits of quantum information needed to store and send data in quantum computing. Others, such as Chris Greene of the University of Colorado, who predicted an earlier type of Rydberg molecule back in 2000, are more skeptical. Greene points out that this hypothetical Rydberg molecule would need to be kept in super-cold temperatures, and its predicted lifespan is still only about a tenth of a second.
Quantum strangeness aside, maybe the most remarkable aspect of these Rydberg molecules - and, indeed , Rydberg atoms as well - is their vast size. Rydberg atoms can be thousands of times bigger than normal molecules, and the Rydberg molecule predicted by Rittenhouse and Sadeghpour could fit a small virus - itself composed of lots of normal-sized molecules - inside it with room to spare.