The Material For BEC *BEC was found in alkali metals e.g.87Rb ()23Na 7Li because: *They are bosons. *Each atom is a small magnetic compass,so that a cooling technique called magnetic cooling can work. *The atoms have a small repulsion,so that they do not liquefy or solidify down to a very low temperature. PDF created with pdfFactory trial version www.pdffactory.com
The Material For BEC ÙBEC was found in alkali metals e.g. 87Rb (铷), 23Na , 7Li because: ÙThey are bosons. ÙEach atom is a small magnetic compass, so that a cooling technique called magnetic cooling can work. ÙThe atoms have a small repulsion, so that they do not liquefy or solidify down to a very low temperature. PDF created with pdfFactory trial version www.pdffactory.com
Cooling I Down the Atoms When the temperature is very low,a large fraction of atoms suddenly crash into the lowest energy state.This is called Bose-Einstein condensation. PDF created with pdfFactory trial version www.pdffactory.com
Cooling Down the Atoms lWhen the temperature is very low, a large fraction of atoms suddenly crash into the lowest energy state. This is called Bose-Einstein condensation. PDF created with pdfFactory trial version www.pdffactory.com
The Strange State of BEC Some atoms in a BEC condensate Some very cold atoms o When all the atoms stay in the condensate,all the atoms are absolutely identical.There is no possible measurement that can tell them apart. o Before condensation,the atoms look like fuzzy balls o After consdensation,the atoms lie exactly on top of each other (a superatom) PDF created with pdfFactory trial version www.pdffactory.com
The Strange State of BEC lWhen all the atoms stay in the condensate, all the atoms are absolutely identical. There is no possible measurement that can tell them apart. lBefore condensation, the atoms look like fuzzy balls. lAfter consdensation, the atoms lie exactly on top of each other (a superatom). PDF created with pdfFactory trial version www.pdffactory.com
How cooling atom? Laser 冷却 Cooling Laser Magnetic Cooling Evapor. Trapping Cooling T 0.18μK ~nK PDF created with pdfFactory trial version www.pdffactory.com
How cooling atom? PDF created with pdfFactory trial version www.pdffactory.com
Laser Cooling BEC Apparatus vacuum pump and Rb source Laser beam Other equipment:laser equipment,computer,electronics Cost less than US$100,000 PDF created with pdfFactory trial version www.pdffactory.com
Laser beam Other equipment: laser equipment, computer, electronics Cost less than US$100,000 Laser Cooling PDF created with pdfFactory trial version www.pdffactory.com