BoseEinsteinkondensation

BoseEinsteinkondensation, commonly referred to as Bose-Einstein condensation (BEC), is a phase of matter that occurs when a dilute gas of bosons is cooled to temperatures near absolute zero. At these temperatures a macroscopic fraction of the particles occupies the lowest quantum state, causing the gas to behave as a single quantum entity. The system develops long-range phase coherence, and in interacting samples can exhibit superfluid-like flow. BEC represents a quantum-degenerate regime in which quantum statistics dominate the collective behavior.

Origin and theory: The idea originated with Satyendra Nath Bose and Albert Einstein in 1924–25, predicting a phase transition for an ideal gas of non-interacting bosons when cooled below a critical temperature. In three dimensions, Tc increases with density and decreases with particle mass; for an ideal gas Tc ≈ (2πħ^2 / (m k_B)) (n / ζ(3/2))^{2/3}.

Experimental realization: In 1995, Eric Cornell and Carl Wieman (Colorado) and Wolfgang Ketterle (MIT) created first atomic BECs using evaporative cooling in magnetic and optical traps with rubidium-87 and sodium-23. Since then BECs have been produced in various atoms and in optical lattices, enabling studies of quantum fluids, interference, and quantum simulation.

Beyond atoms: BEC has been observed for quasi-particles such as exciton-polaritons and photons in dye-filled microcavities; these systems can form condensate-like states at higher temperatures due to driven-dissipative processes.

Significance: BEC provides a platform for precision measurements, interferometry, and quantum simulations of many-body physics. It has advanced the understanding of superfluidity, coherence, and phase transitions.