Many body physics of ultracold quantum gases

Ultracold gases refer to quantum degenerate gases of atoms (such as Rubidium, Potassium or Lithium) or molecules confined in vacuum by laser beams and cooled down to nano-Kelvin temperatures (one billionth degree above absolute zero). These systems offer well-controlled settings to test and advance our basic understanding of the collective behaviors of strongly interacting quantum particles. They can be viewed as the latest breed of quantum matter, trailing a long line of extraordinary examples such as superfluid helium, high temperature superconductors, and antiferromagnets. The research is aimed at expanding our knowledge about quantum phases of matter, and gaining insights for better design and manipulation of quantum materials. We are particularly interested in the quantum phases of Fermi gases in new parameter regimes brought by ongoing cold atoms experiments. Examples of research topics include the exact thermodynamics of low dimensional Fermi gases, topological phases of cold atoms on high orbital bands, as well as the phase diagrams of dipolar Fermi gases. This line of research is currently supported by National Science Foundation, Air Force Office of Scientific Research, and National Institute of Standards and Technology.

Quantum transport in superconducting heterostructures

Superconductivity is a hall mark macroscopic quantum mechanical phenomenon. At low temperatures, many materials become superconductors with vanishing electrical resistance. Moreover, (weak) magnetic field gets expelled from the bulk. A conventional superconductors can be thought as a “perfect” quantum fluid of pairs of electrons, loosely bound together by some attractive interaction between electrons, all sharing the same quantum state. Superconductor has become a leading competitor in building new architects of quantum devices, circuits, and qubits (the fundamental building block for a quantum computer). Our research focuses on superconductors driven out of equilibrium, especially in spatial inhomogeneous systems as found in devices. The goal is to understand the collective, quantum mechanical dance of many electrons when they are driven out of equilibrium. Modeling the dynamics of charge, spin, and energy flow requires techniques such as quantum field theory and nonequilibrium statistical mechanics. Currently, our group is actively studying the hybrid structures of superconductors and topological insulators or other spin-active (magnetic or spin-orbit coupled) materials. Research in this direction may contribute to the next generation quantum devices and circuits that outperform present technologies.