Demagnetization cooling of a gas

Adiabatic demagnetization is an efficient technique forcooling solid samples by several orders of magnitude ina single cooling step. In gases, the required couplingbetween dipolar moments and motion is typically tooweak, but in dipolar gases--of high-spin atoms orheteronuclear molecules with strong electric dipolemoments, for example--the method should be applicable.Here, we demonstrate demagnetization cooling of a gasof ultracold 52Cr atoms. Demagnetization is driven byinelastic dipolar collisions, which couple the motionaldegrees of freedom to the spin degree. In this way,kinetic energy is converted into magnetic work, with aconsequent temperature reduction of the gas. Opticalpumping is used to magnetize the system and drivecontinuous demagnetization cooling. We can increase thephase-space density of our sample by up to one order ofmagnitude, with almost no atom loss, suggesting that themethod could be used to achieve quantumdegeneracy viaoptical means.