Viewpoint Spins in cold atoms — what a drag !

Electron-electron interactions between closely spaced nanoelectronic circuits constitute an alternative coupling mechanism to the inductive and capacitive couplings of conventional electronics. It was realized early on [1, 2] that “Coulomb mutual scattering” between spatially separated electronic systems provides a mechanism for momentum relaxation, which then leads to equalization of drift velocities. This intrinsic friction due to electronelectron interactions is presently referred to as “Coulomb drag” [3–5] and has first been studied experimentally by Gramila et al.[6] and by Sivan, Solomon, and Shtrikman [7] in semiconductor double quantum wells. Now, in a paper in Physical Review Letters, Rembert Duine and Henk Stoof from Utrecht University in the Netherlands add a fresh approach to a different kind of drag physics—the pulling along of spin-aligned ultracold atoms in an optical trap [8].