Brian Anderson, Ph.D. - US grants

This experimental research program is aimed at continuing the advancement of atom optics with explorations of new atom-manipulation methods and potential applications, and with new studies of nonlinear physical phenomena. Quasi-two-dimensional BECs held in optical potentials will be used in three main experiments. In one experiment, quantum point contacts for matter waves will be studied. Using the wide range of configurations afforded by laser light in the creation of atomic potentials, an array of channels for the transport of atoms between two spatially distinct regions will be constructed. The quantum-mechanical nature of these channels will be experimentally characterized, leading to potentially significant and practical atom optics developments. In a second experiment, a quantum state engineering technique analogous to the optical Guoy-phase mode converter will be developed for matter waves. Finally, ring-shaped dark solitons and their modulational instabilities will be studied. The broader impact of the program is in the education of optics graduate students.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

Vortex dynamics in fluids and superfluids lie at the hearts of many important phenomena in physics, including turbulence and the breakdown of superconductivity. While successful models of the bulk properties of such phenomena have been produced, detailed microscopic descriptions that include the roles of vortices have been exceptionally difficult to develop. This NSF award supports research aimed at filling this crucial niche through the experimental study of Bose-Einstein condensates. Made of millions of trapped atoms in an ultracold vapor, Bose-Einstein condensates can be manipulated and detected in the laboratory with microscopic precision, and theoretically understood and modeled with techniques utilizing microscopic descriptions of atomic interactions and quantum mechanics. As the coldest known objects in the universe, dilute-gas condensates also act as coherent fluids and can be used to study fluid and superfluid phenomena in ways not possible before their first experimental observations in 1995. This research program integrates NSF-supported laboratory work with the theoretical efforts of international colleagues into a larger collaborative investigation of turbulence physics, phase transition dynamics, and new vortex creation and manipulation mechanisms in gaseous superfluids.



This work pieces together some of the most difficult parts of the larger puzzle of building a microscopic understanding of vortex behavior, turbulence, and related phenomena in fluids and superfluids. The results of this research are thus expected to have significant and exciting broader impacts in the development of physics as a discipline, and in a wide area of specific fundamental and applied physics topics. By investigating new techniques for vortex manipulation, this study will also develop tools of utility to potential future techniques utilizing quantum-level information processing. As the education of students is certainly one of the most important aspects of federally sponsored research, this project involves undergraduate and graduate students; the education of both groups is key to maintaining national and international strength in science and technology. The majority of this award is allocated to the financial support of graduate students in order to teach these students state-of-the-art experimental techniques in a cutting-edge area of research, and more generally how to do high-quality independent research. These graduate students will carry on a tradition of technical excellence as they eventually merge into other laboratory settings, and will be suited to effectively teach research skills to future generations of graduate students.

A distinction between hydrodynamic turbulence in a bulk fluid, and in one whose flows are restricted to two dimensions, is that energy dissipation at small length scales is generally inhibited in the latter. Under small-length-scale forcing of energy and vorticity into a two-dimensional (2D) fluid, energy is therefore transferred towards larger scales, opposite that of turbulence in a bulk fluid. Most conspicuously, this means that eddies and vortices may merge to form even larger vortices. Two-dimensional quantum turbulence (2DQT) involves the study of 2D turbulence in quantum fluids such as atomic Bose-Einstein condensates (BECs). In this emerging field of research, numerous open questions generally relate to the dynamics of quantized vortices in superfluids and to the distribution of kinetic energy among length scales. For example, do clusters of quantized vortices of identical circulation naturally emerge in 2DQT flows, as initially predicted by Onsager in 1949? This NSF award supports new experiments aimed at understanding the relationships between vortex distributions, vortex dynamics, and energy spectra in 2DQT. The experimental program of research targeting these topics will utilize highly oblate BECs for the construction of a new imaging system designed to observe vortex dynamics within a BEC, the development of on-demand vortex generation and manipulation methods to study vortex interactions in turbulence with a bottom-up approach, and the study and characterization of developed 2DQT in BECs.

Superfluids such as dilute-gas Bose-Einstein condensates have remarkable properties, including frictionless flow and fluid circulation that is obtained only by the formation of many microscopic quantum whirlpools known as vortices. The distribution and dynamics of these vortices throughout the superfluid provide information on fluid phenomena such as turbulence. This project is studying the generation of quantum vortices and follows their dynamics in pancake-shaped condensates as a means to understand the characteristics of two-dimensional turbulence in superfluids. Turbulence in classical fluids is known to share similarities with quantum turbulence in superfluids, but for the specific case of two-dimensional flows, the similarities and differences between the quantum and classical cases are unclear. This grant supports research and graduate-student mentoring and training involving new methods of creating, manipulating, and detecting quantum vortices in condensates, and probes the characteristics of two-dimensional turbulence in these superfluids. Through controlled studies of two-dimensional quantum turbulence, our aim is to develop new insights on vortex interactions and other phenomena of turbulence, one of the most challenging and complex topics in physics.

DESCRIPTION (provided by applicant): Attention selects which aspects of sensory input are brought to awareness. Because attention is a limited resource, which stimuli are attended has important implications for effective goal- directed behavior, survival, and well-being. Attentional selection can proceed in voluntary fashion, according to context-specific goals. At the same time, however, certain kinds of stimuli receive attentional processing involuntarily, overriding goal-directed attention allocation. Such stimuli are said to capture attention. It is well establised that physically salient stimuli capture attention, and that ongoing priorities influence attentiona selection involuntarily through contingent attentional capture. Recently, my colleagues and I have shown that valuable stimuli, previously associated with the delivery of reward, also capture attention involuntarily, independently of salience and ongoing priorities. We have referred to this phenomenon as value-driven attentional capture, and the proposed project will investigate the mechanisms by which learned value influences attentional priority in this way. Aim 1 will probe the mechanisms of selection in value-driven capture using human eye tracking. Through Aim 2, the neural mechanisms of value-driven capture will be assessed using functional magnetic resonance imaging (fMRI), and Aim 3 will investigate the role of value-driven capture in drug addiction. The results will provide a better understanding of the ways in which reward learning influences attentional priority, which represents one of the most critical roles that attention plas in promoting survival. Although attention to reward-predicting stimuli will often be adaptive, it can also become maladaptive when attention to rewarding stimuli conflicts with ongoing goals. In this way, the proposed project will also have important implications for clinical syndromes in which both attention and reward have been critically implicated, including drug addiction, obesity, obsessive-compulsive disorder, and attention-deficit/hyperactivity disorder; these implications will be explored directly in Aim 3. Finally, the proposed project will provide outstanding cutting-edge training in cognitive neuroscience, neuroimaging methodology, and related technical skills, and will continue to develop my strong background in behavioral psychophysics. This award will provide support to complete my dissertation research and prepare me for the next step in my scientific career. PUBLIC HEALTH RELEVANCE: The proposed project investigates the role of reward learning in involuntary attention allocation. Attending to rewarding stimuli is a critical function of the human brain; several clinical conditions, including drug addiction, obesity, obsessive-compulsive disorder, and attention- deficit/hyperactivity disorder, are characterized by disorders of cognitiv control that are thought to involve disordered reward learning. This project will contribute to the basic-research foundations for clinical research into the causes and treatments of these conditions. The findings of the proposed project will also speak to the mechanisms by which people attend to and are distracted by stimuli in their environment, which has public safety implications for issues such as distraction while driving.

At high speeds, fluid flow past an object or through a tube results in turbulence, a chaotic state of flow characterized by unpredictable motion of the vortices or eddies of the flow. Turbulence is ubiquitous, commonly experienced in aircraft or watercraft, observed in rushing rivers, and may be present in blood flow. Yet despite centuries of research on turbulence, this state of fluid flow is one of the least understood phenomena in physics. Discovering its physical origins, and fully characterizing its dynamics and the transition between smooth and turbulent flows, remain significant challenges in physics. Overcoming some of these problems is essential for reaching a deeper understanding of how numerous aspects of our universe evolve. This NSF-funded project experimentally tackles aspects of fluid flows related to turbulence in a special type of fluid for which theoretical and analytical approaches have been developed. In these fluids, called Bose-Einstein condensates (BECs), microscopic droplets of gases cooled to temperatures of a few billionths of a degree above absolute zero, laser light can precisely generate, manipulate, and observe turbulence and the dynamics of the vortices that comprise turbulence. By testing theoretical predictions, this project pushes the boundaries of our understanding of these features of fluid dynamics as they appear in BECs, advancing an understanding of turbulence built up from the most fundamental framework that physicists use to describe the universe, its structure, and its dynamics.

The primary scientific aim of this project is the development of a complete understanding of quantized vortex dynamics in BECs, superfluids for which quantum mechanics governs the dynamics of fluid flow. To achieve this aim, a multi-faceted approach is pursued. First, the project builds on previous work to construct a state-of-the-art microscope designed for and dedicated to observing and measuring vortices and their dynamics directly in BECs. Second, the transition to turbulence in a two-dimensional BEC is studied by examining vortex generation as BECs are stirred by laser light. Results test key theoretical results, and help establish links between quantum and classical fluids. Third, the construction of a toolkit for on-demand creation and manipulation of vortices in a BEC is continued, building on previous successful methods that use moving laser beams to generate and manipulate vortices so that specific arrangements of vortices or types of fluid flow can be created and used on-demand in quantum fluid dynamics experiments. Finally, newly observed methods of vortex nucleation are examined in order to more fully round out an understanding of how vortices and turbulent fluid flows can be generated in BECs. By exploring the dynamics of BEC vortices, this work advances a broader understanding of quantum many-body phenomena in systems with vastly different microscopic properties, such as superfluids, superconductors, and the cores of neutron stars. The project relies on and promotes the scientific education and technical training of students, keys to maintaining national scientific strength and societal breadth and creativity.

PROJECT SUMMARY/ABSTRACT Attention selects which aspects of sensory input receive cognitive processing and thereby influence behavior. Drug addiction alters the attentional system, resulting in prominent attentional biases towards drug cues. Such drug-related attentional biases are related to the broader phenomenology of addiction, including craving and relapse. There has been long-standing interest in implementing attentional bias measures in clinical settings, either as a predictive measure to inform treatment decisions or as a target of treatment. However, a major barrier to the realization of this goal is that current means of assessing these biases are not sufficiently precise to support clinical utility, which has stifled progress in this area. Mirroring this complexity, and underscoring the need for clarity, debate has arisen concerning the role of learning history in the guidance of attention more broadly. Persistent attentional biases have been linked to reward history, learning from aversive outcomes, and outcome-independent selection history (e.g., familiarity). Emerging accounts of such experience-dependent attentional biases disagree about the nature of the underlying mechanism(s) involved. If we do not understand the variety of influences of learning history on attention at a fundamental level, how can we understand how these influences contribute to addiction-related attentional biases? The proposed research directly addresses this need by identifying, isolating, and measuring multiple hypothesized components of the attentional biases that characterize addiction, providing the precision necessary for more accurate predictions of patient outcomes and more targeted efforts to improve these outcomes through attentional bias modification. Specific Aim 1 will distinguish between common and distinct attentional priority signals arising from reward learning and reward-independent selection history, probing both the cognitive and neural mechanisms underlying each of these sources of priority. Specific Aim 2 will identify the cognitive profile and neural mechanisms underlying attentional biases attributable to aversive conditioning, which together with Specific Aim 1 will provide a comprehensive picture of the multifaceted nature of experience-dependent attention. The overarching goal of the proposed research is to characterize multiple distinct components of experience-dependent attentional bias that contribute to attentional biases evident in drug-dependent individuals. These fundamental components of attentional bias will provide a much more precise window into the attentional processes that are relevant to our understanding of addiction than existing measures can offer. It is anticipated that the knowledge gained from the proposed research with provide a foundation for overcoming fundamental limitations in the clinical utility of attentional bias measures, allowing for fruitful exploration of this aspect of addiction in the context of improving assessment and treatment.