For two decades, physicists have predicted the existence of a remarkable family of exotic molecules: giant atoms bound to ordinary atoms, with an electron so distant from its nucleus that it sculpts the pair into bizarre and diverse shapes. Reported in Physical Review Letters, the final member of this “quantum zoo” has been spotted. Led by Herwig Ott at RPTU University Kaiserslautern-Landau in Germany, a team of physicists has created and detected the “butterfly” molecule, completing a 20-year hunt for the elusive structure.
The molecules in this quantum zoo belong to a class known as ultralong-range Rydberg molecules. They form when an ordinary atom becomes bound to a Rydberg atom, whose outermost electron has been excited so far from the nucleus that the atom swells to thousands of times its normal size.
The orbital shapes traced out by these distant electrons give each molecule type its character, and its nickname. Some have elaborate lobed structures reminiscent of trilobites; others spread into the winged outline of a butterfly. These molecules are thousands of times more sensitive to electric fields than ordinary molecules, making them especially useful objects for probing the quantum world.









