A Bose–Einstein condensate (BEC) is a state of matter of a dilute gas of bosons in which the bosonic atoms have condensed into the lowest quantum state, at extremely low temperatures. For typical atomic densities, this condensation occurs at nanokelvin temperatures. In such a condensed state, all particles occupy the same quantum state. As a result of their wave-like nature, several macroscopic phenomena emerge: interference effects due to large occupation numbers; superfluidity with very low viscosity for rotation and flow; and extreme sensitivity to external fields and perturbations.
BECs were first predicted by Indian physicist Satyendra Nath Bose and Albert Einstein in 1924–1925. The original proposal by Bose was not published until 1924, after he had heard about Einstein’s work on stimulated emission. Shortly thereafter, Einstein submitted his own article on the topic, using Bose’s statistical model to derive predictions that were subsequently confirmed experimentally. These developments led to the award of the Nobel Prize in Physics in 1921 to Einstein “for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect”.:239:3 In 1995, Eric Cornell and Carl Wieman created the first true BEC in an atomic vapor, for which they shared half of the 2001 Nobel Prize in Physics with Wolfgang Ketterle “for achievement leading to this breakthrough”.
The existence of BECs relies upon two essential ingredients: long-range attractive interactions between identical bosons (i.e., atoms with integer spin), and sufficiently low temperature so that thermal excitations are negligible. Under these conditions, all atoms collapse into their ground state—the single lowest energy quantum state available—and as a result all atoms occupy exactly the same quantum mechanicalstate. This behavior contrasts sharply with classical physics where subatomic particles move independently unless acted upon by an outside force; it also differs from other phases of matter where molecules or electrons interact only over relatively short distances (such as gases or liquids).