geometric phase

The idea of a pump is at least as old as the ancient Greek philosopher and scientist Archimedes. More than 2000 years ago, Archimedes allegedly invented a corkscrew pump that could lift water up an incline with the turn of a handle. Versions of the ancient invention still bear his name and are used today in agriculture and industry.Modern pumps have achieved loftier feats. For instance, in the late 1990s, NIST developed a device that could pump individual electrons, part of a potential new standard for measuring capacitance.While pumps can be operated mechanically, electrically or via any other source of energy, they all share the common feature of being driven by a periodic action. In the Archimedean pump, that action is a full rotation of the handle, which draws up a certain volume of water. For the NIST electron pump, it is a repeating pattern of voltage signals, which causes electrons to hop one at a time between metallic islands.But physicists have sought for decades to build a different kind of pump—one driven by the same kind of periodic action but made possible only by the bizarre rules of quantum mechanics. Owing to their physics, these pumps would be immune to certain imperfections in their fabrication.Now, a team of physicists working in collaboration with JQI Fellow Ian Spielman and NIST postdoctoral researcher Hsin-I Lu has created just such a pump. By periodically jostling many individual atoms, the researchers were able to shift an entire atomic cloud without any apparent overall motion by its constituents. The team is the first to test this predicted behavior, which arises in what they call a geometric charge pump. The work follows close on the heels of two recent papers that examined topological charge pumps, which demonstrate a distinct but related effect. The new result was published May 20 in Physical Review Letters.