Macroscopic Quantum Phenomena in Bose-Condensed Atomic Gases

Fernando Sols, Sigmund Kohler

Keith R. Burnett, Mark Edwards, Charles W. Clark

Bose-Einstein condensation (BEC) has long been known to be a key element of macroscopic quantum phenomena such as superconductivity and superfluidity. BEC per se, however, eluded direct and unquestioned observation until 1995, when experimental groups produced condensates in dilute atomic alkali gases.

S. Giovanazzi

Farwa Khalid, Mina Vajdi

Superfluidity and Bose-Einstein condensation (BEC) in ultracold atomic gases represent macroscopic quantum phenomena arising from collective particle behavior at near-zero temperatures. Experimental realizations of BEC in alkali gases have enabled the observation of quantized vortices, matter-wave interference, and nonclassical excitations. This article reviews theoretical frameworks including Gross-Pitaevskii and Bogoliubov models, experimental techniques such as evaporative cooling and optical trapping, and computational approaches for simulating condensate dynamics. Two graphical analyses illustrate the condensate density profile and vortex lattice formation. Understanding these phenomena has implications for quantum simulation, atom interferometry, and exploration of quantum hydrodynamics.

C. J. Pethick, H. Smith

C. J. Pethick, H. Smith

Bose–Einstein condensates in dilute atomic gases, which were first realized experimentally in 1995 for rubidium, sodium, and lithium, provide unique opportunities for exploring quantum phenomena on a macroscopic scale. These systems differ from ordinary gases, liquids, and solids in a number of respects, as we shall now illustrate by giving typical values of some physical quantities. The particle density at the centre of a Bose-Einstein condensed atomic cloud is typically 10 13 –10 15 cm −3 . By contrast, the density of molecules in air at room temperature and atmospheric pressure is about 10 19 cm −3 . In liquids and solids the density of atoms is of order 1022 cm −3 , while the density of nucleons in atomic nuclei is about 10 38 cm −3 . To observe quantum phenomena in such low-density systems, the temperature must be of order 10 −5 K or less. This may be contrasted with the temperatures at which quantum phenomena occur in solids and liquids. In solids, quantum effects become strong for electrons in metals below the Fermi temperature, which is typically 10 4 –10 5 K, and for phonons below the De bye temperature, which is typically of order 10 2 K. For the helium liquids, the temperatures required for observing quantum phenomena are of order 1 K. Due to the much higher particle density in atomic nuclei, the corresponding degeneracy temperature is about 10 11 K. The path that led in 1995 to the first realization of Bose–Einstein condensation in dilute gases exploited the powerful methods developed over the past quarter of a century for cooling alkali metal atoms by using lasers.