学术活动发布与订制系统

Understanding the collisions of cold atoms and molecules are an essential aspect of controlling these species for numerous applications in precision measurement, few- or many-body physics, quantum simulation, or novel quantum technologies. Cold collisions not only give rise to coherent interactions for quantum gas control but also can result in loss processes that limit the time scale for such control. These lectures will cover the basic concepts of cold atomic and molecular collisions, including tunable resonant control. Well-studied experimental systems will be used as case studies to illustrate the concepts and to introduce several topics of current research interest.

This lecture describes how to describe cold collisions quantum mechanically, with emphasis on scattering and bound state properties near a collision threshold that are relevant to cold atom studies, emphasizing especially the role of the long range potential between two interacting atoms. The key concept of the scattering length represents a phase shift that gives a unique "quantum personality" to the interactions of a pair of cold atoms and determines the properties of a quantum degenerate cold atomic gas. The 7 isotopes of the Yb atom make a good test case of threshold scattering and bound state properties, and help to illustrate the powerful "quantum defect" concept.

Magnetically tunable scattering resonances known as Feshbach resonances permit the control of the interactions of cold bosonic or fermionic atoms, as demonstrated by a wide variety of applications. This lecture shows how to understand such resonances, for which the dimensionless parameter which characterizes their intrinsic strength ranges over more than 5 order of magnitude among experimentally known resonances . The properties and uses of magnetically tunable Feshbach resonances will be illustrated by examples successfully used in experimental work.

This lecture continues a discussion of Feshbach resonances, introducing two topics relevant to ongoing research. One is overlapping or interfering resonances, which are important in several practical cases of active research. The other is the case of optically tunable resonances, which serve as an example of a class of resonances that exhibit loss due to spontaneous irreversible decay. This lecture shows how to compare optical Feshbach resonances to magnetic ones, and explains the conditions of laser detuning and intensity under which control of the scattering length can be obtained. Light shifts due to off-resonant optical coupling may also control quantum gases with minimal losses.

The concept of "universality,” that is, having scattering properties that are independent of the details of complex short range chemical interactions, is a powerful one in ultracold physics, since only the scattering length is needed to characterize few-body and many-body physics in this domain. Extending the concept to include also the length scale of the long-range potential greatly enhances our understanding, illustrated by precision binding energy measurements, determination of the effective range, and calculation of few-body dynamics. In the case of highly reactive or inelastic molecular collisions, the concept of long-range universality can be extended to understand the magnitude of collisional losses for a broad class of molecular collisions.

The lecture series concludes by exploring some additional topics that are relevant to current research areas. These include chaotic dynamics with complex atoms or molecules, which have dense sets of overlapping resonances but may also have some universal properties. The effect of reduced dimension, or tight quantum confinement, on cold collisions will be examined for some aspects of atomic and molecular collisions.

个人介绍: Paul S. Julienne obtained his Ph. D. in Chemical Physics in 1969 from the University of North Carolina at Chapel Hill. After postdoctoral work at the National Bureau of Standards (NBS), he worked with the Plasma Physics Division at the Naval Research Laboratory before returning to NBS (now called NIST) in 1974, where he has remained ever since. He served as a group leader for the Quantum Processes Group, as a NIST Fellow, and as a founding Fellow of the Joint Quantum Institute (JQI) of NIST and the University of Maryland. After retiring in 2013, he serves as a NIST Scientist Emeritus and an Emeritus Fellow and Adjunct Professor of Physics at the JQI. He is a Fellow of the American Physical Society (APS) and was awarded the 2004 Davisson-Germer Prize of the American Physical Society and the 2015 William F. Meggers Award of the Optical Society of America. Since the mid 1980s, his research has concentrated on the collisions and spectroscopy of cold and ultracold atoms and molecules and their applications in quantum gases and optical lattices.