Cryogenic surface electrode ion traps with integrated superconducting microwave resonators for polar molecular ion spectroscopy

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 129-144).Trapped cold molecules open the possibility of studying ultracold chemistry and astrophysical processes in laboratory settings. Their rich internal structure also makes them suitable for quantum information manipulation or for tests of fundamental laws of nature. These experiments require precise control over the molecular internal degrees of freedom. There are few present proposals for trapping and cooling molecules. One proposal is based on confining neutral polar molecules in DC Stark shift traps, but this approach presents some issues. An attractive alternative is to confine polar molecular ions in RF Paul ion traps, which is the focus of this thesis. The objectives here are to develop the theoretical models and to devise the experimental components and methods to investigate the coupling of polar molecular ions' rotational states to the microwave radiation. The new approach presented here is based on co-trapping Sr+ atomic ions together with SrCl+ molecular ions in a cryogenic surface electrode RF ion trap and on using the coupling of the molecular ion's rotational states to an integrated superconducting microwave line or cavity either as a cooling method or for precise rotational spectroscopy. The first part of the thesis describes two theoretical methods for observing the coupling of the microwave radiation to the rotational levels of a molecule. The first method proposed is based on the enhancement of the molecular rotational transition rates by the co-trapped molecular-atomic ions Coulomb collisions. The second method is based on microwave cavity assisted heating or cooling of the molecular ions. The second part of the thesis presents the development of a cryogenic surface electrode RF ion trap with an integrated microwave transmission line/resonator. The ion trap is operated in a 4.2 K closed cycle cryostat.by Paul Bogdan Antohi.Ph.D

Structure-Preserving Model Reduction of Physical Network Systems

This paper considers physical network systems where the energy storage is naturally associated to the nodes of the graph, while the edges of the graph correspond to static couplings. The first sections deal with the linear case, covering examples such as mass-damper and hydraulic systems, which have a structure that is similar to symmetric consensus dynamics. The last section is concerned with a specific class of nonlinear physical network systems; namely detailed-balanced chemical reaction networks governed by mass action kinetics. In both cases, linear and nonlinear, the structure of the dynamics is similar, and is based on a weighted Laplacian matrix, together with an energy function capturing the energy storage at the nodes. We discuss two methods for structure-preserving model reduction. The first one is clustering; aggregating the nodes of the underlying graph to obtain a reduced graph. The second approach is based on neglecting the energy storage at some of the nodes, and subsequently eliminating those nodes (called Kron reduction).</p