Strides made by our field have tremendously deepened our understanding of ultracold atomic gases in the quantum mechanical realm. Increasingly, these gains are being translated into prospects for controlling atomic behavior, for instance in the development of the next generation of atomic clocks, for creating novel phases of atomic gases for purposes of quantum information technology, and for the manipulation of chemical reaction dynamics. Today, the capability of controlling interatomic interaction in ultracold quantum gases makes this field of research able to predict and realize a wide range of quantum phenomena that encompass a number of different physics subfields, notably atomic and molecular, condensed matter, and nuclear physics. As was fully recognized after the first dilute Bose-Einstein condensates were created, few-body processes have paramount importance, since they dictate the lifetime and stability of condensates as well as their mean-field behavior. Studies included in this project open up ways to explore and control few-body processes in ultracold quantum gases, thereby suggesting the likelihood of a new level of control over chemical reactions, as well as the ability to uncover novel quantum phases and the new ways to produce stable gases in exotic dynamical regimes.
The research plans within the project have an impact on two major fronts. First, control over chemical reactions can be seen as a longstanding goal having far-reaching scientific and technological ramifications. Such control can be used, for instance, to study the role of scattering resonances in chemical reaction dynamics, to explore geometric phase effects in chemical dynamics, and ultimately to control chemical reactivity. Second, the search for novel quantum phases of matter, through the use of controllable interactions, sparks new ways to navigate in one of deepest territories of modern science.
The intellectual merit of this project has derived from the successful development of theoretical and computational tools that have permitted us to understand one of the most fundamental aspects of the universal three-body problem. Universality in this context means that the insights derived from atomic and molecular physics also teach us key aspects about the behavior of very different systems like interacting nucleons, despite the huge difference in energy scales. In particular, we succeeded in finding the reason why experiments were observing an unexpected commonality in the positions of three-body resonances among many different atomic species. Our interpretation began with numerical explorations. Then after confirming the experimental regularities, our mathematical and interpretive toolkit allowed an extraction of the most important result, which was that the commonality was controlled by the long-range van der Waals interaction between atoms. These extensions of theoretical insight and computational capabilities opens up ways to explore and control few-body processes in ultracold quantum gases, thereby bringing the promise of a new level of control over chemical reactions, the ability to uncover novel quantum phases, as well as the ability to provide new ways to produce stable gases in exotic dynamical regimes. Few-body systems pose some of the greatest challenges to theorists in atomic, molecular, and optical physics because of their extremely nonpertubative nature. And at the same time, all the phenomena being studied are accessible to experimental observation, and either have been or are likely to be examined in laboratories in the near future. During the period of this project, we have also succeeded in developing a theoretical description of how five atoms can simultaneously collide and recombine to form bound subsystems, such as a diatomic and triatomic molecule. This process had been thought to be entirely negligible in a dilute atomic gas, far less probable than other recombination pathways involving three or even four atoms. But one surprising outcome of our research has been the demonstration, through a combination of theory and experiment, that regimes exist where the dominant cluster formation mechanism is actually through five-body recombination. Another promising line of research that has been pursued under this funded project is the effect of light fields that are implemented in clever ways to control the manner in which atoms interact with one another. Specifically, our work has developed a theoretical method that can be used to examine the coherent control of three-body processes by external fields. The formulation has been developed and this understanding has been transferred to our numerical algorithms and computer codes. This formulation combines the hyperspherical representation and the Floquet representation and has been shown to be accurate while also offering a simple and conceptually clear physical picture. Today, we can calculate two- and three-body properties under influence of radio-frequency and optical external fields. The above description of the intellectual merit also feeds into the broader impacts of this work. One of the most interesting aspects of current studies of ultracold atoms and molecules is that they frequently serve to elucidate phenomena observed in quite different fields and under highly varied conditions. Thus the fact that the newly observed universality of the three-body parameter in atomic physics is now understood to have no analogous counterpart in nuclear systems is a deeper implication that extends beyond the traditional scientific arena of cold atom research. Another broader impact of this and all other research carried out in this group is the training component. Introducing new theoretical tools and ideas to the next generation of physicists is among the most vital aspects of research funding in this field. In the case of the current grant, one completed PhD dissertation has been primarily supported by this grant, and part-time support has helped other graduate students and postdoctoral associates to learn about these methods and to push them farther. Through their creativity and hard work, they in turn push the boundaries of what is possible in this area of physics.
