Nonclassical dynamics of Bose condensates in an optical lattice in the superfluid regime

A condensate in an optical lattice, prepared in the ground state of the superfluid regime, is stimulated first by suddenly increasing the optical lattice amplitude and then, after a waiting time, by abruptly decreasing this amplitude to its initial value. Thus the system is first taken to the Mott regime and then back to the initial superfluid regime. We show that, as a consequence of this nonadiabatic process, the system falls into a configuration far from equilibrium whose superfluid order parameter is described in terms of a particular superposition of Glauber coherent states that we derive. We also show that the classical equations of motion describing the time evolution of this system are inequivalent to the standard discrete nonlinear Schreodinger equations. By numerically integrating such equations with several initial conditions, we show that the system loses coherence, becoming insulating.Comment: 5 pages, 4 figure

Binary Mixtures of Bose-Einstein Condensates: Phase dynamics and Spatial Dynamics

We investigate the relative phase coherence properties and the occurrence of demixing instabilities for two mutually interacting and time evolving Bose-Einstein condensates in traps. Our treatment naturally includes the additional decoherence effect due to fluctuations in the total number of particles. Analytical results are presented for the breathe-together solution, an extension of previously known scaling solution to the case of a binary mixture of condensates. When the three coupling constants describing the elastic interactions among the atoms in the two states are close to each other, a dramatic increase of the phase coherence time is predicted. Numerical results are presented for the parameters of the recent JILA experiments.Comment: 19 pages, 3 figures, final version of the pape

Social Diffusion and Global Drift on Networks

We study a mathematical model of social diffusion on a symmetric weighted network where individual nodes' states gradually assimilate to local social norms made by their neighbors' average states. Unlike physical diffusion, this process is not state conservational and thus the global state of the network (i.e., sum of node states) will drift. The asymptotic average node state will be the average of initial node states weighted by their strengths. Here we show that, while the global state is not conserved in this process, the inner product of strength and state vectors is conserved instead, and perfect positive correlation between node states and local averages of their self/neighbor strength ratios always results in upward (or at least neutral) global drift. We also show that the strength assortativity negatively affects the speed of homogenization. Based on these findings, we propose an adaptive link weight adjustment method to achieve the highest upward global drift by increasing the strength-state correlation. The effectiveness of the method was confirmed through numerical simulations and implications for real-world social applications are discussed.Comment: 7 pages, 3 figures; to appear in Phys. Rev.

Phase Dynamics of Bose-Einstein Condensates: Losses versus Revivals

In the absence of losses the phase of a Bose-Einstein condensate undergoes collapses and revivals in time due to elastic atomic interactions. As experiments necessarily involve inelastic collisions, we develop a model to describe the phase dynamics of the condensates in presence of collisional losses. We find that a few inelastic processes are sufficient to damp the revivals of the phase. For this reason the observability of phase revivals for present experimental conditions is limited to condensates with a few hundreds of atoms.Comment: 24 pages, 9 figures. submitted to European Journal of Physics

A Comparative Analysis of the Capacity-building Industries in Pittsburgh and Central Texas

Five years ago, The Forbes Funds provided support for a new research series exploring challenges and strategic opportunities in nonprofit management in the Pittsburgh region.The intention of this research was to determine what works in strengthening nonprofits' organizational capacity and management abilities, as well as what may be the barriers or service gaps in building nonprofit capacity. As part of this research series, in 2004,The Forbes Funds commissioned Judith L. Millesen, at Ohio University, and Angela L. Bies, at Texas A&M University, to conduct a comprehensive analysis of Pittsburgh's capacity-building "industry." This "Pittsburgh study" offered detailed findings about the degree to which Pittsburgh's "industry of consultants, firms, management support organizations, and academic centers offer accessible, quality services to the 1,600 nonprofit organizations in Allegheny County."1 With ongoing support from The Forbes Funds, Drs. Bies and Millesen also conducted continuing analyses during 2005, which explored the incentive to engage in capacity building (Millesen & Bies, 2005) and the role of 'learning' in building nonprofit performance (Bies & Millesen, 2005).During 2005-06, a replication study was conducted in and around Austin,Texas.2 A key purpose of the study was to help afford a comparative analysis of the nonprofit sectors in two metropolitan regions with differing environments, economies, and capacity-building industries. With support from The Forbes Funds, the Bremer Foundation, and the Minnesota Council on Nonprofits, a third replication study is planned for 2006-07 in the Minneapolis-St. Paul area.The Texas replication study shared the Pittsburgh study's focus on understanding the characteristics of effective capacity-building initiatives through an examination of a series of questions related to who (the capacity builders) is doing what (the kinds of support services provided) for whom (what types of nonprofits are engaging in capacity-building initiatives) and to what end (whether capacity-building initiatives produce desired organizational change).The core research purpose remained to describe and analyze several aspects of the capacity-building environment, including the quantity, accessibility, and quality of capacity building services, characteristics of effective capacity building, and challenges and barriers to implementing capacity-building interventions. Both the Austin study and the Pittsburgh study offered implications for practice and suggested directions for future research into capacity building's effectiveness and influence in the sector

Spin-squeezed atomic crystal

We propose a method to obtain a regular arrangement of two-level atoms in a three-dimensional optical lattice with unit filling, where all the atoms share internal state coherence and metrologically useful quantum correlations. Such a spin-squeezed atomic crystal is obtained by adiabatically raising an optical lattice in an interacting two-component Bose-Einstein condensate. The scheme could be directly implemented on a microwave transition with state-of-the art techniques and used in optical-lattice atomic clocks with bosonic atoms to strongly suppress the collisional shift and benefit from the spins quantum correlations at the same time