Rydberg atoms are atoms in which one or more electrons are excited to very high energy levels, far from the nucleus. These highly excited states mean the electron orbits at a much larger distance than usual, sometimes hundreds or thousands of times farther than in the ground state.
Because the electron is so loosely bound, Rydberg atoms exhibit exaggerated quantum properties. For example, they have enormous sizes, long lifetimes, and extreme sensitivity to electric and magnetic fields. Their large electric dipole moments lead to strong interactions with nearby atoms, enabling phenomena like dipole blockade, which is important for quantum information processing.
These unusual features make Rydberg atoms valuable for precision measurements, studying quantum many-body physics, and developing quantum technologies such as quantum simulators and quantum gates.