Dynamics of evaporative cooling in magnetically trapped atomic hydrogen

We study the evaporative cooling of magnetically trapped atomic hydrogen on the basis of the kinetic theory of a Bose gas. The dynamics of trapped atoms is described by the coupled differential equations, considering both the evaporation and dipolar spin relaxation processes. The numerical time-evolution calculations quantitatively agree with the recent experiment of Bose-Einstein condensation with atomic hydrogen. It is demonstrated that the balance between evaporative cooling and heating due to dipolar relaxation limits the number of condensates to 9x10^8 and the corresponding condensate fraction to a small value of 4% as observed experimentally.Comment: 5 pages, REVTeX, 3 eps figures, Phys. Rev. A in pres

Optimization of evaporative cooling towards a large number of Bose-Einstein condensed atoms

We study the optimization of evaporative cooling in trapped bosonic atoms on the basis of quantum kinetic theory of a Bose gas. The optimized cooling trajectory for $^{87}$Rb atoms indicates that the acceleration of evaporative cooling around the transition point of Bose-Einstein condensation is very effective against loss of trapped atoms caused by three-body recombination. The number of condensed atoms is largely enhanced by the optimization, more than two orders of magnitude in our present calculation using relevant experimental parameters, as compared with the typical value given by the conventional evaporative cooling where the frequency of radio-frequency magnetic field is swept exponentially. In addition to this optimized cooling, it is also shown that highly efficient evaporative cooling can be achieved by an initial exponential and then a rapid linear sweep of frequency.Comment: 7 pages, REVTeX, 5 eps figures, Phys. Rev A in press (01 Feburuary 2003

Interference between electromagnetically induced transparency and two-step excitation in three-level ladder systems

We have performed electromagnetically induced transparency (EIT) and two-photon absorption experiments in ladder-type three-level systems in a hot sodium atomic vapor, using the 3S1/2-3P1/2-4D3/2, 3S1/2-3P3/2-4D3/2,5/2, 3S1/2-3P1/2-5S1/2, and 3S1/2-3P3/2-5S1/2 transitions. In particular, in the most pronounced 3S1/2-3P1/2-4D3/2 system, we have observed quite unique spectral line shapes that are superpositions of sharp dips and peaks, in contrast to ordinary EIT spectra. The peaks and dips have apparently different physical origins, and the line shape can be interpreted as the interference between EIT and two-step excitation