Magneto-optical traps

Figure C 1.4.8. (a) An energy level diagram showing the shift of Zeeman levels as the atom moves away from the z = 0 axis. The atom encounters a restoring force in either direction from counteriDropagating light beams, (b) A typical optical arrangement for implementation of a magneto-optical trap.

Early experiments witli MOT-trapped atoms were carried out by initially slowing an atomic beam to load tire trap [20, 21]. Later, a continuous uncooled source was used for tliat purjDose, suggesting tliat tire trap could be loaded witli tire slow atoms of a room-temperature vapour [22]. The next advance in tire development of magneto-optical trapping was tire introduction of tire vapour-cell magneto-optical trap (VCMOT). This variation captures cold atoms directly from the low-velocity edge of tire Maxwell-Boltzmann distribution always present in a cell... 

Fig. 13.16a. As an atom source, a magneto-optical trap (MOT) for cold Cs-atoms was used. The fluorescence of MOT atoms around the MNF was detected by the measurement of fluorescence photons with an avalanche photodiode connected to one end of the fiber. Signals are accumulated and recorded on a PC using a photon-counting.

Fig. 13.16 (a) Experiment on detection of atomic clouds with an MNF. APD is the avalanche photodiode. MOT is the magneto optical trap, (b) Coupling efficiency of spontaneous emission into each direction of nanofiber propagation mode, tyg, vs. atom position rla, where r and a are distance from nanofiber axis and radius of nanofiber, respectively. Reprinted from Ref. 21 with permission. 2008 Optical Society of America... 

Fig. 20 shows the resonances observed in a magneto-optical trap at 300 pK by scanning the static electric field for four different densities. As in the previous case of the cesium atom, the resonances are broader than expected for the dipole-dipole interaction alone. We have to take into account the migration processes of the excitation of the reaction products... 

Recent progress in the atomic microchips industry, has stimulated great interest in studies of neutral ultracold gases [Lin 2004], The ultra cold atomic samples are typically produced in magneto-optical traps, then loaded into ei-... 

MOT Magneto Optical Trap. The well established technique for Doppler cooling and trapping of a thermal cloud of cold atoms. 

Where does this spectacular development lead concerning frequency standards Traps for neutral atoms unfortunately perturb the atomic energy levels both the magnetic fields used as well as the laser light for cooling. As an example of what can be achieved, mention may be made of a tuneable dye laser, locked to the intercombination line at 657 nm of Ca atoms, either in an atomic beam or in a magneto-optic trap, has an estimated relative uncertainty of below 10 [38]. 

Atoms in an optical trap (Doppler cooling Wineland, et al., 1978 optical molasses Chu, et al., 1986 magneto-optic trap Steane and Foot, 1991 Helmerson, et al., 1992) are confined and cooled to translational temperatures on the order of << 1 mK. Ultracold collisions between such trapped atoms permit the recording of bound<—free spectra with resolution limited only by the translational temperature (1 mK, which corresponds to a frequency resolution of 7 x 10-4 cm-1) (Julienne and Mies, 1989 Lett, et al., 1995 Burnett, et al., 2002). This makes spectroscopically accessible the extremely long-range regions of potential energy curves (R >10A 5Re) and otherwise only indirectly observable weakly bound or repulsive electronic states. 

Leonhardt D and Weiner J 1995 Direct two-color photoassociative ionization in a rubidium magneto-optic trap... 

Fig. 9.21 Magneto-optical trap, (a) Optical molasses inside the center of an inhomogeneous magnetic field (b) preparation of one of the three laser beams (c) level scheme illustrating the principle of the MOT (d) potential of the MOT (e) schematic experimental setup...

The reservoir for the cold atom can be either a magneto-optical trap or a BEC. A short laser pulse with a wavelength tuned to the atomic absorption line travelling into the +z-direction pushes the atoms out of the trap. The recoil momenrnm hvic gives the atoms the initial velocity vo = h- vl mc). 

Gabbanini, C., Fioretti, A., Lucchesini, A., Gozzini, S., and Mazzoni, M., Cold rubidium molecules formed in a magneto-optical trap, Phys. Rev. Lett, 84, 2814, 2000. 

Brown, B.L., Dicks, A.J., and Walmsley, LA., Coherent control of ultracold molecule dynamics in a magneto-optical trap by use of chirped femtosecond laser pulses, Phys. Rev. Lett., 96, 173002, 2006. 

ZUio, S.C., Marcassa, L., Muniz, S., Horowicz, R., Bagnato, V., Napolitano, R., Weiner, J., and Julieime, P.S., Polarization dependence of optical suppression in photoassocia-tive ionization collisions in a sodium magneto-optic trap, Phys. Rev. Lett., 76, 2033, 1996. 

A very elegant experimental realization for cooling and trapping of atoms is the magneto-optical trap (MOT), which is based on a combination of optical molasses and an inhomogeneous magnetic quadrupole field (Fig. 14.18). Its principle can be understood as follows ... 

---