Bose-Einstein Condensation and Atom Lasers

In sufficiently cold and dense atomic samples, where the thermal de Broglie wavelength becomes comparable to the mean separation between the atoms, so-called Bose-Einstein condensation (BEC) can occur. In this case the atomic matter waves overlap and the indistinguishability of atoms becomes 

In 1998 BEC in spin-polarized hydrogen, the most long-rmming candidate, was also achieved [9.466] using an efiicient combination of magnetic trapping and evaporative coohng [9.457]. 

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Proceedings Bose-Einstein Condensates and Atom Lasers... 

S. Martelucci (ed.), Bose-Einstein Condensates and Atom Laser (Kluwer Academic, New York, 2000) ... 

In this section we discuss the new technique of optical cooling, which decreases the velocity of atoms to a small interval around v = 0. Optical cooling down to temperatures of a few micro Kelvin has been achieved by combining optical and evaporative cooling even the nanoKelvin range was reached. This brought the discovery of quite new phenomena, such as Bose-Einstein condensation or atom-lasers, and atomic fountains [1109-1 111]. 

Currently, a major theme in atomic, molecular, and optical physics is coherent control of quantum states. This theme is manifested in a number of topics such as atom interferometry, Bose-Einstein condensation and the atom laser, cavity QED, quantum confutation, quantum-state engineering, wavepacket dynamics, and coherent control of chemical reactions. 

This positive development is partly based on new experimental techniques, such as improvements of existing lasers and the invention of new laser types, the realization of optical parametric oscillators and amplifiers in the femtosecond range, the generation of attosecond pulses, the revolution in the measurements of absolute optical frequencies and phases of optical waves using the optical Ifequency comb, or the different methods developed for the generation of Bose-Einstein condensates of atoms and molecules and the demonstration of atom lasers as a particle equivalent to photon lasers. 

Ketterle, W., Nobel lecture When atoms behave as waves Bose-Einstein condensation and the atom laser. Rev. Mod Phys., 74, 1131, 2002. 

The trapping of cold neutral atoms is a powerful tool in experimental atomic physics that has made it possible to conduct many fundamental experiments, such as Bose Einstein condensation and the production of Fermi-degenerate quantmn gases. It is therefore one of the most vivid demonstrations of the capabilities inherent in the laser control of atoms. 

The realization of Bose-Einstein condensation and the atom laser has opened up an opportunity to observe and use in experiments the coherent properties of atomic matter. Coherent atomic sources can be used for the purposes of atom interferometry and holography. A direct observation of interference in a BEC was made in an experiment by Andrews et al. (1997). A BEC cloud obtained from with 5 x 10 sodium atoms was cut by a blue-detuned laser beam into two parts. The two parts of the condensate were then released from the trap. In the course of their free expansion, the two parts of the BEC overlapped and produced an interference pattern, which was probed by absorption imaging. The interference fringes showed good contrast, thus pointing to the conservation of long-range order in the condensates. 

Concurrently, the world of ultracold systems has expanded its boundaries during the last decade to encompass ultracold, three-dimensional, large hnite systems [e.g., ( He)jy clusters (N = 2-10" ), and ( He)jy clusters (N = 25-10 )] in the temperature range of T = 0.1-2.2 K [6-11, 50-78], finite optical molasses in laser irradiated ultracold atomic gases in the temperature range of 10-100 pK [79], as well as finite Bose-Einstein condensates in the temperature range of 10-100 nK [14, 80],... 

Bose-Einstein condensate a state of matter, produced in laboratories, in which atoms are packed so close together that their wavefunctions become correlated similar to those of photons in a laser beam, and coherent matter waves can be formed. 

The increasing research on laser cooling of atoms and molecules and many experiments with Bose-Einstein condensates have brought about some remarkable results... 

The development of techniques for cooling and trapping of atoms has led to great advances in physics, which have already been recognized by two Nobel prizes. In 1997 the prize was jointly awarded to Steven Chu, Claude Cohen-Tannoudji, and William D. Phillips for their developments of methods to cool and trap atoms with laser light [1-3]. In 2001, Eric A. Cornell, Wolfgang Ketterle, and Carl E. Wieman jointly received the Nobel prize for the achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates [4,5]. 

The increasing research on laser cooling of atoms and molecules and many experiments with Bose-Einstein condensates have brought about some remarkable results and have considerably increased our knowledge about the interaction of light with matter on a microscopic scale and the interatomic interactions at very low temperatures. Also the realization of coherent matter waves (atom lasers) and investigations of interference effects between matter waves have proved fundamental aspects of quantum mechanics. 

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