Description:

Professor Erhai Zhao, Geroge Mason University 

Title: Hunting for spin liquids in an ultracold quantum gas

Abstract: Quantum spin liquids evade conventional long-range order down to zero temperature. These highly entangled states do not break any symmetry and have unique properties including possible topological order or fractional excitations. They are hard to come by not only in real materials but also in theoretical models. After a brief review of known model systems that potentially harbor spin liquid, I will introduce a new model, the dipolar Heisenberg model, motivated by recent experiments on ultracold dipolar molecules and atoms with large magnetic moments. I will present arguments why competing orders and frustration suppress long range order. Then I will sketch two methods used to obtain the phase diagrams of dipolar Heisenberg model on the square and triangular lattice, one based on tensor network wave functions, and the other based on functional renormalization group. Both methods yield evidence for a quantum paramagnetic ground state occupying an extended region of the phase diagram. By comparing to DMRG, I will argue that it is likely a quantum spin liquid. These large scale numerics are made possible by using NVIDIA GPU cards. I will briefly describe our adventure with this massively parallel computing framework originally designed for video gaming and now powering a significant portion of artificial intelligence research.

Host: Jim Sauls