This award supports theoretical research and education at the interface of condensed matter physics and atomic physics. The PI will address fundamental issues in four major areas in quantum gases: (i) strongly interacting Fermi gases, (ii) quantum gases in optical lattices, (iii) quantum gases with internal degrees of freedom, and (iv) fast rotating quantum gases. These projects are directly related to current experiments. At the same time, they explore new directions.
The projects on Fermi gases will study universal properties of these systems, and their generalization to non-zero rotations and two dimensions. The goal is to develop new exact relations that will shed light on thermodynamic and transport properties. The projects on lattice quantum gases address two very important issues: how to reduce entropy substantially so as to reach the strongly correlated regime efficiently, and to determine the phase diagram of the system directly from experimental data. The projects of large spin quantum gas will help us uncover new macroscopic quantum phenomena and to explore the intrinsic dipolar effects in these systems. They will help design and engineer special quantum spin states in these systems in the future. The study of fast rotating quantum gases is aimed to realize quantum Hall states in ultra-cold atoms.
These projects will provide training for students and postdoctoral researchers in different areas, for example condensed matter physics, atomic physics, and quantum optics.
NONTECHNICAL SUMMARY This award supports theoretical research and education at the interface of condensed matter physics and atomic physics. The PI will study new quantum mechanical states of matter exhibited by atoms cooled to very low temperature and trapped, for example by laser light. Rotating gases of ultracold atoms will also be studied. Some states of matter of ultracold atom systems have analogies with electronic states of matter that occur in complex materials and in electrons in a high magnetic field that are confined to two dimensions in semiconducting materials. The synergy among the studies of trapped ultracold atoms and condensed matter systems may lead to more rapid advance on challenging fundamental scientific problems. While ultracold atoms and electronic systems are each interesting in their own right, understanding these systems in each case has the potential to lead to future computing and device technologies.
This project also provides opportunities for advanced education and contributes to the highly skilled scientific workforce of the 21st century.
This NSF funded project studies the properties of dilute quantum gases at ultra low temperatures. Such gases, which are prepared at temperatures 100 million times lower than room temperature, are now of great interest to physicists for a number of reasons. Firstly, at such extremely low temperatures, these gases behave very coherently and together magnify the phenomena in the atomic world on a grand scale, allowing physicists to view quantum phenomena much easily. Secondly, such cold atoms can be put in a lattice of light. In such settings, the cold atoms behave like electrons in crystals. We can therefore use the cold atom system to model various aspects of solid state matters and come up with ideas to help design materials. Thirdly, neural atoms have internal degrees of freedom (called spin), and many of them have spins much large than that of electrons in solids. As a result, there is a much greater variety of novel matter that can be made out at atoms with large spins than those by electrons in solids. In this project, we study how interactions between ultra-cold atoms affect their collective behavior, how to successfully simulate electronic matters using cold atoms, and how to create novel matter using atoms with large spins. Our studies have identified the conditions under which strong repulsion will turn a quantum gas into a ferromagnet, even though it remains a gas. We have also identify the conditions for a mixture of different quantum gases to phase separate, a phenomena also related to ``ferromagnetism". Our work has helped settle a recent controversy on the discovery of ferromagnetism in a strongly repulsive Fermi gas. In our study of quantum gases in lattices made of light (the so-called optical lattice), we have come up with methods to cool quantum gases down to the temperature regimes necessary to simulate electronic matters. In addition, we have also come up with algorithms to deduce the properties of solid state systems from the observed density profile of a tiny quantum gas in a trap. Experimental groups in University of Chicago and in ENS (Paris) have shown that our algorithms are very powerful. In our study of quantum gases with internal degrees of freedom, we have discovered a new kind of ``condensed" state of ultra-cold atoms when an artificial spin dependent electro-magnetic field (so-called spin-orbit coupling) is introduced to the system. Our predictions on the phase diagram were later verified by the experimental group at NIST. We have also come up with methods to overcome the severe heating problem in current experiments on spin-orbit coupling in quantum gases. These NSF supported research has led to 51 invited talks in international conferences and major institutions. For outreach, the P.I. has also given a public lecture to 1000 high school students in the large convention center in Hong Kong in 2009. These NSF funded projects have provided good training of three students and two postdoc associates. Three of these associates are now faculty members in the major academic institutes in Hong Kong and in Beijing. One former student is now a postdoc at University of Maryland, and other student will be getting his Ph.D degree in a year.
