Applications of Cooled Atoms and Molecules

Collisions between cold atoms in a trap can be studied experimentally by measuring the loss rate of trapped atoms under various trap conditions (temperature, magnetic-field gradients, light intensity, etc.). It turns out that 

Another application is the deflection of atoms by photon recoil. For sufficiently good beam collimation, the deflection from single photons can be detected. The distribution of the transverse-velocity components contains information about the statistics of photon absorption [14.63]. Such experiments have successfully demonstrated the antibunching characteristics of photon absorption [14.64]. The photon statistic is directly manifest in the momentum distribution of the deflected atoms [14.65]. Optical collimation by radial recoil can considerably decrease the divergence of atomic beams and thus the beam intensity. This allows experiments in crossed beams that could not be performed before because of a lack of intensity. 

A very interesting application of cold trapped atoms is their use for an optical frequency standard [14.66]. They offer two major advantages reduction of the Doppler effect and prolonged interaction times on the order of 1 s or more. Optical frequency standards may be realized either by atoms in optical traps or by atomic fountains [14.67]. 

For the realization of an atomic fountain, cold atoms are released in the vertical direction out of an atomic trap. They are decelerated by the gravitational field and return back after having passed the culmination point with V. = 0. 

Assume the atoms start with vq = 5 m/s. Their upward flight time is then t = Oz/S = 0-5 s, their path length is z = VQt — gt /2 = 1.25 m, and their total flight time is 1 s. Their transit time through a laser beam with the diameter = 1 cm close to the culmination point is Tu- = 90 ms, and the maximum transverse velocity is u 0.45 m/s. The transit-time broadening is then less than 10 Hz. 

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