The term "Rydberg atom" refers to an atom in a highly excited state where one or more of its electrons are in a Rydberg orbital. A Rydberg atom is characterized by having an electron orbit that is much farther from the nucleus compared to the typical electron orbits in ground state or lower energy states.
The concept is named after the Swedish physicist Johannes Rydberg, who made significant contributions to the understanding of atomic spectra and the mathematical relationships governing the spectral lines. In particular, Rydberg developed the Rydberg formula, which describes the wavelengths of spectral lines emitted or absorbed by hydrogen atoms.
In a Rydberg atom, the principal quantum number (n) of the electron's orbit is very large, leading to an electron that is highly "excited" and positioned far from the nucleus. Rydberg atoms are known for exhibiting unique and distinctive properties, including exaggerated sensitivity to external electric and magnetic fields, long lifetimes in certain states, and the ability to undergo Rydberg-Rydberg interactions.
Rydberg atoms are of interest in various areas of physics, including atomic and molecular physics, quantum optics, and studies of ultracold gases. They are often used in experiments exploring quantum phenomena, quantum information processing, and quantum simulation due to their intriguing properties and behaviors in highly excited states.