Pairing in an off-kilter atomic gas

Abstract

Physics In a process called Cooper pairing, two electrons of opposite spin and momentum form a pair and join a larger “condensate” to flow effortlessly through a superconducting material. In cold atomic gases, the atomic state plays the role of the spin. But what happens if there is a different number of atoms in the two spin states, so that pairing cannot be perfect? Ong et al. tackled that question for 6Li atoms trapped in a weakly coupled array of pancakeshaped clouds. As they cranked up the interaction between the atoms and increased the relative number of minority spins, the gas in each pancake separated into a core of paired spins surrounded by the majority atoms. Phys. Rev. Lett. 114 , 110403 (2015).