Jun 28 2005
MITscientists have brought a supercool end to a heated race among physicists: They have become the first to create a new type of matter, a gas of atoms that shows high-temperature superfluidity.
他们的工作在6月23日的自然问题中，与金属中电子的超导性密切相关。Superfluids的观察可能有助于解决关于高温超导性的挥之不去的问题，这对于MIT集团来说，诺贝尔·克雷特（John D. Macarthur物理学教授。
Seeing the superfluid gas so clearly is such a dramatic step that Dan Kleppner, director of the MIT-Harvard Center for Ultracold Atoms, said, "This is not a smoking gun for superfluidity. This is a canon."
几年来，世界各地的研究群体一直在研究所谓的Fermionic原子的冷气，以找到新形式的超浊度的最终目标。超流体可以在不抵抗的情况下流动。当它旋转时，可以清楚地区分正常气体。正常气体像普通物体一样旋转，但是超流度只能在形成类似于迷你龙卷风的涡流时旋转。这使得旋转的超流体旋转的瑞士奶酪的外观，其中孔是迷你龙卷风的核心。“当我们看到电脑屏幕上的涡旋的第一张照片时，它只是令人惊叹的是，”研究生·Zwierlein召回了4月13日晚上，当球队首先看到超流量气体时，称。近一年来，该团队一直在努力使磁场和激光束非常圆，因此气体可以旋转。“这就像打开一个轮子的凸起，使其完美地使其变得完美，”Zwierlein解释说。
“在Superfluids以及超导体中，粒子在锁骨中移动。它们形成一个大量机械波，”ketterl欧洲杯猜球平台e说明。这种运动允许超导体承载电流而不会阻力。
The MIT team was able to view these superfluid vortices at extremely cold temperatures, when the fermionic gas was cooled to about 50 billionths of a degree Kelvin, very close to absolute zero (-273 degrees C or -459 degrees F). "It may sound strange to call superfluidity at 50 nanokelvin high-temperature superfluidity, but what matters is the temperature normalized by the density of the particles," Ketterle said. "We have now achieved by far the highest temperature ever." Scaled up to the density of electrons in a metal, the superfluid transition temperature in atomic gases would be higher than room temperature.
Ketterle's team members were MIT graduate students Zwierlein, Andre Schirotzek, and Christian Schunck, all of whom are members of the Center for Ultracold Atoms, as well as former graduate student Jamil Abo-Shaeer.
The team observed fermionic superfluidity in the lithium-6 isotope comprising three protons, three neutrons and three electrons. Since the total number of constituents is odd, lithium-6 is a fermion. Using laser and evaporative cooling techniques, they cooled the gas close to absolute zero. They then trapped the gas in the focus of an infrared laser beam; the electric and magnetic fields of the infrared light held the atoms in place. The last step was to spin a green laser beam around the gas to set it into rotation. A shadow picture of the cloud showed its superfluid behavior: The cloud was pierced by a regular array of vortices, each about the same size.
这项工作基于麻省理工学院组的早期创建Bose-Einstein凝聚液，一种物质的形式，其中颗粒浓缩并充当一个大波。欧洲杯猜球平台阿尔伯特爱因斯坦于1925年预测了这种现象。后来科学家意识到Bose-Einstein凝聚和超浊度密切相关。
Bose-Einstein condensation of pairs of fermions that were bound together loosely as molecules was observed in November 2003 by independent teams at the University of Colorado at Boulder, the University of Innsbruck in Austria and at MIT. However, observing Bose-Einstein condensation is not the same as observing superfluidity. Further studies were done by these groups and at the Ecole Normale Superieure in Paris, Duke University and Rice University, but evidence for superfluidity was ambiguous or indirect.
在麻省理工学院创建的超流度FERMI气体也可以作为易于控制的模型系统，以研究诸如早期宇宙中存在的固体超导体，中子恒星或夸克 - 胶质等离子体的诸如固体超导体，中子恒星或夸克 - 胶质等离子体的诸如实心超导体，中子恒星或夸克 - 胶质等离子体的性质。
http://web.mit.edu/