Chill atoms almost to absolute zero and they start acting as one.
In 1924 Satyendra Nath Bose and Albert Einstein predicted a strange state of matter: cool certain atoms enough and they all drop into the same quantum state, behaving like a single giant wave. It took 70 years and temperatures around 170 billionths of a degree above absolute zero to make one.
The story began when the Indian physicist Satyendra Nath Bose sent Einstein a paper deriving the law of radiation from a new way of counting particles of light. Einstein was so impressed that he translated it into German himself and had it published in 1924. He then extended Bose's reasoning to atoms. Particles of a certain type, now called bosons, are allowed to share the same quantum state, and Einstein predicted that if they were cooled enough, many would 'condense' into the lowest available state, forming a new kind of matter.
In such a condensate, quantum effects that are normally confined to the microscopic world become visible at a larger scale: the atoms' waves overlap and behave as one. In 1938 Fritz London suggested this was behind the frictionless flow of superfluid helium. But making a pure condensate from a gas proved fiendishly hard. Four research groups chasing it with hydrogen from 1976 onwards struggled, and hydrogen was only condensed in 1998.
The first success came on 5 June 1995, when Eric Cornell and Carl Wieman in Boulder, Colorado, cooled around two thousand rubidium atoms to below about 170 nanokelvin using lasers and magnetic evaporative cooling. Wolfgang Ketterle at MIT did it with sodium a few months later. The three shared the 2001 Nobel Prize in Physics.
Hundreds of labs now make condensates routinely. They have been used to show interference between clouds of atoms, to create quantum whirlpools, and, in a 1999 Harvard experiment led by Lene Hau, to slow a light pulse to about 17 metres per second. In 2020 the Cold Atom Laboratory made one aboard the International Space Station, where free fall lets the atoms be observed for over a second.
Source: Wikipedia — Bose–Einstein condensate · Text summarised from Wikipedia (CC BY-SA 4.0)
