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(共15张PPT)
玻色-爱因斯坦凝聚
玻色-爱因斯坦凝聚
一、理想玻色气体化学势的性质
二、Ｎ 与基态粒子数
关键在于当
时，将
上的粒子数忽略了.
解决办法:
三、矛盾的原因与解决办法
当 时，该能级上的粒子数与总粒子数相比，可忽略；
而 时，该能级上的粒子数是很大的数值，不可忽略。
1.0
1.0
0
基态粒子比份
T ＞ TC 　　弥散态
T ＜ TC 　　凝结态
T ＝ TC　　　 相变点
T 0　　 全部凝结
玻色－爱因斯坦凝聚
2.条件
a.玻色子
b. 随温度而改变，且随温度降低趋向于0
1.现象： 时，有宏观量级的粒子在零能级凝聚
玻色凝聚：μ = 0 , n0与n可比
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弥散态 (动量空间) 凝聚态
动量空间的凝聚现象,凝聚体的熵为零，对压强无贡献
四、凝聚相下，
内能由能量大于0的粒子决定
玻色－爱因斯坦凝聚的实现
(1) Low temperature T ~ 10–9 (e.g. Rb)
Cooling and trapping atoms
(2) Higher density n ~ 1011-12
Trapping atoms by using laser
(3) System keeps in the gas phase
(Non-interaction)
The Nobel Prize in Physics 1997
"for development of methods to cool and trap atoms with laser light"
Stanford Univ.
Stanford, CA, USA
b. 1948
Collège de France and cole Nornale Supérieure
Paris, France
b. 1933
National Institute of Standards and technology , MD, USA
b. 1948
Their research is helping us to study fundamental phenomena and measure important physical quantities with unprecedented precision.
Claude Cohen-Tannoudji
Steven Chu
William D. Phillips
1980s when William Phillips developed new methods of decelerating a fast atom beam. In 1985 the first reports came from experiments where the mean velocity had been reduced from 1000 m/s to zero.
Deceleration of Atoms
　MOT The most often used for atom trap is the Magneto-Optical Trap (MOT).
　　Steven Chu used Doppler cooling with three pairs of counter-propagating laser beams. Atom, regardless of what direction it is moving, will encounter a friction force and the velocity spread (and the temperature) will be reduced　optical Molasses.
A collection of sodium atoms (yellow dot in middle of picture) trapped in a MOT.
Light acts mechanically on material objects, to change their positions and velocities.
Laser reduces the velocity spread (cooling), or confine the atoms (trapping).
New cooling mechanisms
Explanations of the low temperatures were found by
Claude Cohen-Tannoudji and by Steven Chu.
Greek mythology has it that Sisyphus must endlessly roll a stone up a hill in the Underworld. As soon as he reaches the top the stone rolls down again.
One example of the new cooling mechanisms is Sisyphus cooling, where the concepts of light shift and optical pumping play an important role.
Sisyphus cooling
Cohen-Tannoudji
developed the following physical picture:
10-6K
The atoms move on a sinusoi-
dally modulated potential surface, when they interact with light (light shift).
When they travel 'uphill' they lose speed. As they reach the top of the 'hill' they are optically pumped to the bottom of a 'valley'.
In this way the atoms will always travel 'uphill', and thus their velocity will gradually be reduced.
继续降温
玻色凝结
The Nobel Prize in Physics 2001
"for the achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates"
Eric A. Cornell
USA
University of Colorado, JILA
Boulder, CO, USA
b. 1961
Wolfgang Ketterle
FRG
MIT,
Cambridge, MA, USA
b. 1957
Carl E. Wieman
USA
University of Colorado, JILA
Boulder, CO, USA
b. 1951
Program
Get firstly a great deal of Bose atoms
with high density and cooled temperature
(Laser cooling and trapping technology)
Put the sample in a static magnetic well
(Magnetic trapping)
Chilling evaporatively the atom gas
(Evaporatively chilling technology)
Observing condensation
(Resonant absorption)
Rubidium (Rb) 1995
Eric A. Cornell
Carl E. Wieman

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