Prof. Han Pu's research interest is in the field of theoretical ultracold atomic physics, which covers different aspects of the physics of Bose-Einstein condensation, quantum degenerate Fermi gases, quantum optics and laser cooling and trapping. One of the most profound revolutions brought about by quantum mechanics is that it does away with the distinction between particles and waves: atoms, in particular, can exhibit all the properties that we associate with wave phenomena when cooled to ultracold temperatures. The development of these ideas leads to the emergence of the field of atom optics, a highly inter-disciplinary field with close ties to atomic physics, quantum optics, quantum information and condensed matter physics.
One of the particular systems we have studied is the so-called spinor condensate, an atomic condensate with spin degrees of freedom. Due to the nonlinear spin-exchange interaction, this system exhibits a variety of interesting behavior. Because of the close relation between atomic spin and its magnetic moment, a spinor condensate also represents a novel magnetic material. The effect of the long-range magnetic dipole-dipole interaction on the system is currently under study in our group. Another system we are interested in involves quantized vortices, which is a hallmark of superfluid and occurs in such diverse fields as superconductors, superfluids, quantum magnets, liquid crystals, nuclear matters, etc. The novelty of the atomic systems lies in the fact that these systems are very clean with great experimental controllability, such that their properties can be exquisitely tailored and manipulated. We are interested in a number of phenomena displayed by cold atoms related to vortex matter, such as the ground state structures, dynamics, collective excitations, quantum phase transitions, quantum melting of vortex lattices, etc. Besides cold atoms, we are also interested in cold molecules, which are not merely a natural extension of the former, but possess many compelling properties of their own. In particular, we are interested in its formation and dissociation dynamics. A key feature in this system is the role played by quantum statistics --- the properties are sensitive to whether the constituent atoms are bosons or fermions.
In the past few years, considerable advances have been made in learning how to create and manipulate matter waves. Now it is time to ask how we can use them. The study of ultracold atomic physics, on the one hand, touches the very fundamentals of quantum mechanics with broader impact in other fields such as condensed matter physics; on the other hand, also shows great promises in applications such as ultra-precision measurement, time standard, weak signal detection, quantum computing, etc.