By manipulating the behavior of particles at a quantum level, scientists at the Joint Quantum Institute (JQI, a research partnership of NIST and the University of Maryland) have caused a tiny cloud of cold atoms to change position – without any apparent motion by its constituents. The result* is what they call a "geometric charge pump," and it provides long-anticipated confirmation of behavior predicted over 30 years ago.
A short animation demonstrating the atomic motion that drives small shifts in a cold cloud of atoms. As the energy potential (blue) is varied periodically, atoms are tipped between atomic states (green and yellow). Although the density of atoms in each cell remains the same, the entire cloud (orange) drifts to the right.
The experiment involves shining interfering lasers onto a Bose-Einstein condensate of rubidium atoms, forming an optical lattice that traps the atoms into local sites. The researchers can adjust the power of the lasers and an applied magnetic field, which changes the energy potential "felt" by the atoms. By varying these parameters in a periodic way, they coax atoms into tipping back and forth between adjacent sites in the lattice. Although at the end of each cycle the atoms see the same energy potential as they started in, they accumulate some quantum phase change with each cycle, corresponding to an overall spatial shift in the cloud of atoms.
"These cold atoms are a useful platform to study theoretical ideas that can't be tested with ordinary condensed matter systems," says NIST physicist and author Ian Spielman. In this case, it is unclear how to experimentally create periodic variations in the structure of a crystal lattice. He notes that exploring such behavior in a cold atom system could eventually enable similar techniques in other physical platforms.
To read more visit http://jqi.umd.edu/news/quantum-cycles-power-cold-atom-pump