Many Facets of Laser-Atom and Dipole-Dipole Interactions

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There has been substantial recent progress using atoms and ions as the working elements in quantum computers and quantum simulators. In addition, there are several proposals to use controlled atoms or ions in complex arrangements to manipulate properties of laser light. Studies of this type are being aggressively pursued in Europe and Asia, and the ability of the US to compete in this arena could be crucial for several technologies. This project will attempt to better simulate several common processes in quantum computers and/or simulators that are often treated in an approximate manner; the goal is to predict which properties are important for a successful quantum computer. In addition, the group will explore the role that cooperative affects among atoms play in these systems and whether the many interactions lead to qualitatively different outcomes. The basic understanding of these systems is difficult; and will require the development of new tools that could be of widespread utility. Because the operation of quantum computers or simulators depends on fragile quantum processes, it is important to understand how the atoms or ions and the lasers interact at a fine level of detail. Even small effects can accumulate over the many atoms or ions and lead to failure. Thus, a major drive of this project is to reduce the approximations in order to reliably predict how these machines will operate.The goal of the projects in this proposal is to understand how small, but possibly important, effects will limit the effectiveness of quantum computers, will control how light is manipulated through the interaction with patterned arrays of atoms, or will display interesting collective phenomena due to the long range dipole-dipole interaction between atoms. One set of projects addresses how the interaction of light with atoms in quantum computers can lead to entanglement of the center of mass motion of the atom with its internal states, which can be a source of decoherence; this entanglement is caused by the momentum kick of photon absorption and/or emission. A second set of projects simulates, at a more detailed level than performed to date, how a patterned array of atoms can manipulate, for example, the direction of a light beam; for example, each photon reflecting from the array must give a momentum kick but whether the kick is coherently or is incoherently spread over several atoms has not been investigated. A last group of projects is proposed to understand basic physics processes that arise when many atoms interact with light; as an example, many atom coherences can develop within the ground state when it has angular momentum greater than zero. The overarching goal for all projects is to investigate complex quantum phenomena involving many particles where the interaction between them is through the retarded and quantized electromagnetic field. Another interest is in understanding how complex behavior can emerge from simple interactions and, thus, could be of wide interest.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.