This award supports research and education in theoretical physics in an area related to the interaction of ultracold atoms and molecules with surfaces. The award is supported by DMR and a partnership with NSF EPSCoR. The research addresses the theoretical challenge of non-perturbatively describing the dynamics of a quantum system that is strongly coupled to a continuum of surface and bulk excitations. A multichannel formulation of inelastic quantum scattering will be extended and applied to quantum sticking and desorption. Using Fredholm theory for systems of coupled integral equations and diagrammatic perturbation theory, asymptotic solutions will be sought in the low energy regime. Within the multichannel formalism developed, novel multiphonon resonances recently seen in numerical calculations of the Debye-Waller factor will be analyzed, and the effects of non-zero substrate temperature will be explored. The behavior of the probability of sticking as the particle energy tends to zero?the threshold law for quantum sticking?will be calculated for a variety of model coupling forms and potentials having application to physical systems that include: (1) neutral atoms impinging on helium-II, (2) neutral atoms impinging on simple metals, (3) a Bose-Einstein condensate (BEC) impinging on a dielectric substrate, (4) charged atoms impinging on dielectric substrates, and (5) charged atoms impinging on simple metals. Efforts will focus on the possibility of threshold laws deviating from those ascribed to quantum reflection. Investigations will include threshold effects stemming from many-body effects (1) of the final state such as the infrared catastrophe, and (2) of nonlinear interactions in the case of the BEC.
The research has a strong education component involving the training of graduate students and a continuation of the PI's long history of recruiting undergraduates in cutting edge research projects with publishable outcomes.
NON-TECHNICAL SUMMARY: This award supports fundamental theoretical research and education on the quantum physics related to the interaction of ultracold atoms and molecules with surfaces. The award is supported by DMR and a partnership with NSF EPSCoR. The research is grounded in the usual quantum phenomena observed when very low energy objects are propelled towards a surface and bounce off. This is exactly the opposite of classical systems where attractions between surfaces and nearby object causes them to stick, at least when the speed of the object is extremely small. This phenomenon of a perfect quantum bounce has moved from the status of an intellectual curiosity to one of central importance in the field of cold atom research and the associated relevance of that to nanotechnology. Advances in this area of cold atom research can be crucial for developing new miniaturized atom chips in which atoms are trapped less than a micron or so from the surface.
This research will be conducted with the participation of graduate and undergraduate students who will be trained in modern methods of theory with applications to nanotechnology, preparing them for careers in science and nanotechnology. The research will be performed in collaboration with scientists from the US and abroad, strengthening and enriching the US physical community.
The adsorption of atoms and molecules on surfaces is fundamental to surface science. It is the first step in the epitaxial growth of thin films. It is important in catalysis where adsorbates can increase or decrease the surface reaction rate. Many important technologies sensitively depend on the way that adsorbates interact with surfaces. A partial list includes lubrication, coatings and sensors. Several important properties of solids are shaped by how their surfaces interact with adsorbates. Corrosion of metals depends crucially on the interaction of adsorbates with surfaces. Advances in atomic and molecular beam physics has led to the development of techniques to probe dynamical properties of surfaces. The accurate interpretation of experimental data rests on having a quantum theory of adsorption and general inelastic particle-surface interactions. This grant supported further developments in the quantum theory of scattering and sticking of cold atoms and molecules by surfaces. Addressing the intellectual merits of this project, our work has culminated in the discovery of new threshold laws for adsorption and has been detailed in several high profile publications and at lectures at domestic and international conferences. We discovered that a quantum phase transition can change a sticky surface to a perfectly reflecting one for cold atoms. The work has potential applications to the emerging field of atom optics, where ultracold matter waves are controlled and processed in a similar way to light waves in conventional optics. In terms of broader impacts, the grant supported two graduate students who successfully completed all degree requirements for graduation: Ms. Yanting Zhang (Ph.D. 2012) who is now a staff member at IBM, and Mr. Ian Goyette (M.S. 2011) who is now on the staff of ExoAnalytics in Irvine, CA. The work has also supported scientific outreach through public events, lectures and interactive presentations held at the ECHO Science Center in Burlington, Vermont.
