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Experiments and Theory in Ultracold Collision Dynamics

J. Weiner

Published Oct 1, 1997• 0 citations
OpenAlex

Abstract

Abstract : This research program seeks to understand and control atomic collisions at ultracold temperatures where quantum and light-filed effects lead to new interactions between atoms. We have pursued experimental and theoretical investigations of optical shielding and suppression, and the nature of ground-state collisions in and near a Bose-Einstein condensate. This research shows how inelastic collisions can be turned on and turned off by light fields, how the scattering length of ultracold ground-state collisions might be altered by light fields.

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Abstract : This research program seeks to understand and control atomic collisions at ultracold temperatures where quantum and light-filed effects lead to new interactions between atoms. We have pursued experimental and theoretical investigations of optical shielding and suppression, and the nature of ground-state collisions in and near a Bose-Einstein condensate. This research shows how inelastic collisions can be turned on and turned off by light fields, how the scattering length of ultracold ground-state collisions might be altered by light fields.
Two recent developments in ultracold atomic collision physics are discussed. The first is the “optical shielding” of ultracold atomic collisions by optical radiation that is tuned to the blue of an atomic resonance. This radiation couples a pair of colliding atoms to repulsive excited states and prevents their close approach. This effect may substantially suppress inelastic collision rates, and is an interesting example of the control of a cold collision process by a weak perturbing field. The second topic is ultracold atom photoassociation spectroscopy. In this work, high resolution free‐bound absorption spectra are obtained which provide detailed information on the long‐range states of the two interacting atoms. The physics of these states has an appealing simplicity, and in addition is of importance for a complete understanding of the effects of atomic interactions in cold atom experiments. The photoassociation spectra also provide a unique probe of cold collisions.
Cold and ultracold collisions occupy a strategic position at the intersection of several powerful themes of current research in chemical physics, in atomic, molecular and optical physics, and even in condensed matter. The nature of these collisions has important consequences for optical manipulation of inelastic and reactive processes, precision measurement of molecular and atomic properties, matter-wave coherences and quantum-statistical condensates of dilute, weakly interacting atoms. This crucial position explains the wide interest and explosive growth of the field since its inception in 1987. The author reviews elements of the quantum theory of scattering theory, collisions taking place in the presence of one or more light fields, and collisions in the dark, below the photon recoil limit imposed by the presence of any light field. Finally, it reviews the essential properties of these mesoscopic quantum systems and describes the key importance of the scattering length to condensate stability.
Cold and ultracold collisions occupy a strategic position at the intersection of several powerful themes of current research in chemical physics, in atomic, molecular and optical physics, and even in condensed matter. The nature of these collisions has important consequences for optical manipulation of inelastic and reactive processes, precision measurement of molecular and atomic properties, matter–wave coherences and quantum-statistical condensates of dilute, weakly interacting atoms. This crucial position explains the wide interest and explosive growth of the field since its inception in 1987. The author reviews elements of the quantum theory of scattering theory, collisions taking place in the presence of one or more light fields, and collisions in the dark, below the photon recoil limit imposed by the presence of any light field. Finally, it reviews the essential properties of these mesoscopic quantum systems and describes the key importance of the scattering length to condensate stability.
A series of experiments investigating ultracold collision dynamics are performed. In particular, I investigate a number of new methods by which lasers may increase or decrease inelastic collision rates. The experiments are performed in a Rb magneto-optical trap (MOT). In addition, the dynamics of excited-ground ultracold collisions are investigated in the temporal domain. Semiclassical simulations of the collision processes are performed to provide a simple, intuitive model for ultracold collisions in the presence of laser light. ^
Research focusing on the formation of ultracold atomic and molecular quantum gases is a continuously expanding field due to its envisioned applications such as quantum-controlled chemistry or quantum simulation. The aim of our theoretical work is to find ways to suppress inelastic or reactive processes between colliding particles in ultracold quantum gases. Using a laser field detuned to the blue of a relevant transition, we propose to couple the initial colliding particle state to a repulsive excited one, thus preventing the particles to come close to each other. This "blueshielding" technique is applied for ultracold quantum gases, close to quantum degeneracy. We investigate the optical shielding in ultracold39K-Cs collision by using close-coupling channel method. As the (3)3Σ+and (2)3Π+molecular states are repulsive in long range[1], one verified effective optical shielding can be realized via driving the transition from the ground α3Σ+state to these excited states in the presence of linear-polarized light. We demonstrate that a strong field with a small blue detuning to the atomic transition is to the benefit of shielding since the Condon point is farther away from the inner region of ground triplet state. The spontaneous emission effect is taken into account by considering excited optical potentials with the modified formula of shielding rate [2]. We expect the shielding efficiency could be improved by using circular-polarized light [3].
The authors review progress in understanding the nature of atomic collisions occurring at temperatures ranging from the millidegrees Kelvin to the nanodegrees Kelvin regime. The review includes advances in experiments with atom beams, light traps, and purely magnetic traps. Semiclassical and fully quantal theories are described and their appropriate applicability assessed. The review divides the subject into two principal categories: collisions in the presence of one or more light fields and ground-state collisions in the dark.