毕业答辩模板-华中师范大学汉口分校.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * for the achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates http://www.nobel.se/physics/laureates/2001/index.html * * * * * * * * Evaporative Cooling (挥发冷却) Principle: Evaporation takes heat. A cup of tea gets cool after steam escapes, because faster atoms escape from the cup, leaving behind the slower ones. Technique: Lower the height of the trap quickly, so that there are still enough atoms left in the trap to get involved in BEC. Try to trap the largest number of atoms in BEC in the animation: /physics/2000/bec/evap_cool.html Can You Break This Record? Q3: What Does a Bose-Einstein Condensate Look Like? There is a drop of condensate at the centre. The condensate is surrounded by uncondensed gas atoms. The combination looks like a cherry with a pit. See the movie when it cools from 400 nK to 50 nK (1 nK= 10-9K). : /physics/2000/bec/what_it_looks_like.html The Nobel Prize in Physics 2001 USA(Eric A.Cornell,1961) Germany(Wolfgang Kettlerle,1957) USA(Carl E.Wieman,1951) “for the achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates What is an atom laser? An atom laser is analogous to an optical laser, but it emits matter waves instead of electromagnetic waves. Its output is a coherent matter wave, a beam of atoms which can be focused to a pinpoint or can be collimated to travel large distances without spreading. The beam is coherent, which means, for instance, that atom laser beams can interfere with each other. Compared to an ordinary beam of atoms, the beam of an atom laser is extremely bright. One can describe laser-like atoms as atoms marching in lockstep. Although there is no rigorous definition for the atom laser (or, for that matter, an optical laser), all people agree that brightness and coherence are the es