Ultracold Gases Flowing without Friction
Yong-il Shin, Seoul National University

When the many parts of a system interact, sometimes very surprising behaviors are generated in the whole system, which are not found in the parts themselves. This is called an emergent phenomenon and has been often observed in many complex systems. In everyday life, one can appreciate it by seeing how brave things can be done by a group of kids when they are together. Tiny particles like electrons or atoms might be presented as simple and well-understood objects but when many of them compose a system, some special correlations between them could be built up by their quantum-mechanical interactions, leading to strange emergent behavior of the whole system. The most well-known example is a superconductor discovered at very low temperature, where electric currents flow without resistance. Understanding and controlling of emergent phenomena in quantum many-body systems is one of the chal- lenging goals in physics.

In this presentation, I will introduce a research field of ultracold quantum gases, where we cool down dilute gases of atoms and mol- ecules to nano-Kelvin temperatures and study quantum many-body phenomena including superfluidity and quantum magnetism. Because of their low particle densities 100,000 times less than that of air, the system remains gaseous at that extremely low tem- perature. Quantum statistics and interactions profoundly change their properties and below a certain critical temperature, they can undergo a phase transition to a remarkable state of matter called a superfluid, which has no resistance to flow. Deciphering of the key correlations in emergent phenomena is generally a very difficult problem due to the complexity of many-body systems. Ultracold gas systems provide a valuable laboratory to study quantum phenomena because the isolated atoms can be observed and manipulated with the precision and control of atomic physics, while the forces between them are accurately known. This is a crucial advantage for comparing experimental findings with theoretical models. As an example of the major achievements made in this research field, I will briefly discuss on resonantly interacting Fermi gases where a high temperature fermionic superfluid was observed.

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