Physics and Astrophysics Yen Lee at 4 p.m. Friday, Feb. 17, in 211 Witmer Hall for a lecture titled "Ultracold Atoms in Optical Lattices: The Quest for Antiferromagnetism." Coffee and Cookies will be served at 3:30 p.m. 215 Witmer Hall.

Abstract: Recent advances have made it possible to prepare clouds of atoms at temperatures of about 0.0000000004 Kelvin – less than a billionth of a degree above absolute zero.  At such low temperatures the atoms reveal their quantum mechanical wave nature, marching in lockstep to produce novel phases of matter.  The density, composition, disorder, interactions, and lattice potential can be all be controlled independently using lasers and magnetic fields.  Ultracold atomic gases hold great promise for precision measurement (clocks), quantum computing, and the emulation of condensed matter systems such as the Fermi Hubbard model, which may apply to high-temperature superconductors.

The Fermi Hubbard model has now been realized using potassium-40 atoms in optical lattices.  However, the average entropy is rather high (S/N ≈ 1 kB/atom).  Our quantum Monte Carlo simulations suggest that antiferromagnetic order begins to develop below S/N ≈ 0.65 kB/atom, which may be achievable with current techniques.  However, lower entropies are required for robust antiferromagnetism.  I have proposed a way to attain very low temperatures and entropies (≾ 0.03 kB/atom) by trapping fermions in a corral formed from another species of atoms.  This Fermi system can then be evolved into an antiferromagnet by morphing the lattice into a set of double wells, quasi-adiabatically.  Quantum dynamics simulations have, so far, given promising results.