title: Spin gradient thermometry for ultracold atoms in optical lattices.
abstract: We demonstrate spin gradient thermometry, a new general method of measuring the temperature of ultracold atoms in optical lattices. We realize a mixture of spins separated by a magnetic field gradient. Measurement of the width of the transition layer between the two spin domains serves as a new method of thermometry which is observed to work over a broad range of lattice depths and temperatures, including in the Mott insulator regime. We demonstrate the thermometry using ultracold rubidium atoms, and suggest that interesting spin physics can be realized in this system. The lowest measured temperature is 1 nK, indicating that the system has reached the quantum regime, where insulating shells are separated by superfluid layers.
authors.affiliation: MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Weld
authors.forename: Patrick
authors.initials: P
authors.lastname: Medley
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Miyake
authors.forename: David
authors.initials: D
authors.lastname: Hucul
authors.forename: David E
authors.initials: DE
authors.lastname: Pritchard
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Ketterle