Spin gradient demagnetization cooling of ultracold atoms

TL;DR

This paper introduces a novel cooling technique using a time-varying magnetic field gradient to achieve record-low temperatures in ultracold atoms, facilitating quantum simulation of spin Hamiltonians.

Contribution

The authors demonstrate a new spin gradient demagnetization cooling method that reaches unprecedented ultracold temperatures in atomic systems.

Findings

Achieved spin temperatures of +/-50 picokelvin.

Cooled rubidium atoms in a Mott insulator to 350 picokelvin.

Established lowest temperatures ever measured in any system.

Abstract

A major goal of ultracold atomic physics is quantum simulation of spin Hamiltonians in optical lattices. Progress towards this goal requires the attainment of extremely low temperatures. Here we demonstrate a new cooling method which consists of applying a time-varying magnetic field gradient to a spin mixture of ultracold atoms. We have used this method to prepare isolated spin distributions at positive and negative spin temperatures of +/-50 picokelvin. The spin system can also be used to cool other degrees of freedom, and we have used this coupling to reduce the temperature of an apparently equilibrated sample of rubidium atoms in a Mott insulating state to 350 picokelvin. These are the lowest temperatures ever measured in any system.