<B>Faculty Candidate Seminar</B><br><i>Thermometry and Cooling with Ultracold Spin Mixtures in Optical Lattices</i>

Speaker: David Weld (Research Scientist, M.I.T.)

Ultracold atoms in optical lattices are expected to exhibit correlated magnetic quantum phases, but only below a Curie or Néel temperature which is typically less than 1 nanoKelvin. Realization and measurement of this low temperature is the most challenging obstacle on the path towards quantum simulation of spin Hamiltonians in optical lattices. We use a two-component mixture of rubidium atoms in a 3D lattice to demonstrate a new type of thermometry called spin gradient thermometry, which allows direct measurement of a broad range of temperatures in the Mott insulator. Furthermore, we show that this system enables a powerful new cooling technique analogous to adiabatic demagnetization refrigeration. We present initial results of adiabatic demagnetization cooling experiments, which have achieved temperatures of 350 picoKelvin, lower than any ever measured in any system.  We discuss prospects for the use of these techniques to observe magnetic phase transitions in the atomic Mott insulator.