242 Magnetic trapping, evaporative cooling and Bose–Einstein condensation
Fig. 10.15Atoms coupled out of a
Bose–Einstein condensate fall down-
wards under gravity to form a well-
collimated matter-wave beam, with
analogous properties to the beam of
light from a laser. Courtesy of Nathan
Smith and William Heathcote, Physics
department, University of Oxford.
100 mμ10.7.4 The atom laser
The phrase ‘atom laser’ has been used to describe the coherent beam of
matter waves coupled out of a Bose–Einstein condensate (as shown in
Fig. 10.15). After forming the condensate, the radio-frequency radiation
was tuned to a frequency that drives a transition to an untrapped state
(e.g.MF= 0) for atoms at a position inside the condensate. (This comes
from the same source of radiation used for evaporative cooling.) These
atoms fall downwards under gravity to form the beam seen in the figure.
These matter waves coupled out of the condensate have a well-defined(^47) The atoms accelerate as they fall un- phase and wavelength like the light from a laser. (^47) Many novel matter-
der gravity so the wave propagation is
different to that of light.
wave experiments have been made possible by Bose–Einstein condensa-
tion, e.g. the observation of nonlinear processes analogous to nonlinear
optics experiments that were made possible by the high-intensity light
produced by lasers.
10.8 Conclusions
Bose–Einstein condensation in dilute alkali vapours was first observed in
1995 by groups at JILA (in Boulder, Colorado) and at MIT, using laser
cooling, magnetic trapping and evaporation. This breakthrough, and
the many subsequent new experiments that it made possible, led to the
award of the Nobel prize to Eric Cornell, Carl Wieman and Wolfgang
Ketterle in 2001 (and the Nobel prize web site has much useful informa-
tion on this subject, with links to the web sites of the research groups).
Recent BEC experiments have produced a wealth of beautiful images;
however, the objective of this chapter has not been to cover everything
but rather to explain the general principles of the underlying physics.
The two books on BEC by Pethick and Smith (2001) and Pitaevskii and
Stringari (2003) contain much more detail.