Bose-Einstein condensate

A Bose–Einstein condensate is a state of matter in which a large fraction of identical bosons collapse together into the single lowest-energy quantum state. It happens only at extraordinarily cold temperatures, often a millionth of a degree above absolute zero, when the particles are moving so slowly that their quantum wave natures spread out and overlap. Once that overlap is complete, the separate atoms can no longer be thought of as distinct; they share one common wavefunction and act as a single coherent quantum entity.

Albert Einstein predicted this collapse in 1924–25, building on Satyendra Nath Bose's work, but it long seemed too delicate to ever realise. The technical leap came in 1995, when Eric Cornell, Carl Wieman, and independently Wolfgang Ketterle used lasers and magnetic traps to chill dilute gases of rubidium and sodium atoms cold enough to condense. Their achievement won the 2001 Nobel Prize and opened a whole field of ultracold-atom physics.

A condensate makes microscopic quantum behaviour visible on a human scale. Because all the atoms occupy one state, properties that are usually hidden — interference, coherence, even superfluid flow without friction — appear in a cloud you can image directly. Condensates are now used to test fundamental physics, to build exquisitely sensitive sensors, and to simulate the behaviour of harder-to-study quantum systems.