The work of several PI researchers has been chosen for inclusion in the New Journal of Physics (NJP) Best of 2008 issue, which showcases the diversity, breadth and quality of articles published in the journal over the past year. The works were selected on the basis of criteria including referee endorsements, citation and download levels, and broad appeal.
“The resource theory of quantum reference frames: manipulations and monotones,” by Perimeter Institute Faculty member Robert Spekkens, and Gilad Gour, of the University of Calgary, was first published in the March 2008 issue. The paper considers the situation where a reference frame for some particular group of transformations is lacking. In this case, a quantum state that is non-invariant under the action of the group is a resource because it serves as a token of the missing reference frame. For instance, if Bob doesn’t have a sample of Alice’s Cartesian frame, then there are certain operations he cannot do, such as measuring the spin along Alice’s z axis, or rotating a system by 15 degrees about her x axis. But given a token of her frame, such as a pair of spins pointing along her z and x axes, he can approximate these operations. The article explores the extent to which different states of a quantum reference frame may be converted one to the other and distilled into some standard form. It also introduces measures of the quality of a quantum reference frame. A theory of how one can measure and manipulate quantum reference frames should be useful for the field of metrology where the best gyroscopes, time standards, gravitometers, etcetera are likely to soon make use of quantum technology. The work is part of a larger project of exploring basic questions about a diversity of physical resources, of which entanglement and quantum reference frames are but two examples, in the hope of achieving deeper insight through generality.
“Area–angle variables for general relativity,” by past Postdoctoral Fellows Bianca Dittrich and Simone Speziale was published in the August, 2008 issue. It introduced a modified Regge calculus for general relativity on a triangulated four-dimensional Riemannian manifold, an approach which may have applications to classical discrete gravity and non-perturbative approaches to quantum gravity. Dr. Speziale was recently appointed Charge de Recherche at the Centre de Physique Théoretique (CPT) in Marseille. Dr. Dittrich is now a Junior Research Leader at the Max Planck Institute in Berlin.