The first successful Bose–Einstein condensate in a dilute gas, created in 1995, used rubidium-87 atoms.
Eric Cornell and Carl Wieman produced the condensate at JILA in Boulder, Colorado, by cooling rubidium-87 gas to temperatures extremely close to absolute zero. At those temperatures, a large group of atoms occupies the same lowest-energy quantum state and behaves collectively like a single matter wave.
The achievement confirmed a prediction made by Satyendra Nath Bose and Albert Einstein decades earlier. Bose developed the statistics for particles with integer spin, and Einstein extended the idea to predict condensation in a dilute gas.
Rubidium-87 was especially useful because it could be cooled and trapped with established laser-cooling techniques. Wolfgang Ketterle’s group soon created a condensate using sodium-23, and Cornell, Wieman, and Ketterle shared the 2001 Nobel Prize in Physics.