Dark Energy and Projective Symmetry

Nurowski [arXiv:1003.1503] has recently suggested a link between the observation of Dark Energy in cosmology and the projective equivalence of certain Friedman-Lemaitre-Robertson-Walker (FLRW) metrics. Specifically, he points out that two FLRW metrics with the same unparameterized geodesics have their energy densities differing by a constant. From this he queries whether the existence of dark energy is meaningful. We point out that physical observables in cosmology are not projectively invariant and we relate the projective symmetry uncovered by Nurowski to some previous work on projective equivalence in cosmology

Energetics and Possible Formation and Decay Mechanisms of Vortices in Helium Nanodroplets

The energy and angular momentum of both straight and curved vortex states of a helium nanodroplet are examined as a function of droplet size. For droplets in the size range of many experiments, it is found that during the pickup of heavy solutes, a significant fraction of events deposit sufficient energy and angular momentum to form a straight vortex line. Curved vortex lines exist down to nearly zero angular momentum and energy, and thus could in principle form in almost any collision. Further, the coalescence of smaller droplets during the cooling by expansion could also deposit sufficient angular momentum to form vortex lines. Despite their high energy, most vortices are predicted to be stable at the final temperature (0.38 K) of helium nanodroplets due to lack of decay channels that conserve both energy and angular momentum.Comment: 10 pages, 8 figures, RevTex 4, submitted to Phys. Rev.

HEAT CAPACITY OF NEODYMIUM BELOW 10 K

La chaleur spécifique d'un mono-cristal de Néodyme, placé dans un champ magnétique (0 - 1,3 T), est étudiée dans le domaine de température de 1,5 à 10 K. On observe une structure plus détaillée dans les transitions successives que dans les observations précédentes et une forte dépendance de cette structure avec l'histoire thermique de l'échantillon.We report results on the heat capacity of a single crystal of Neodymium in the temperature range 1.5 - 10 K and in applied magnetic fields 0 - 1.3 T. We observe considerably more structure than has previously been seen and some strong dependence on the thermal history

Properties of high-quality coplanar waveguide resonators for QIP and detector applications

We have fabricated and characterized λ/2 thin-film coplanar waveguide resonators made from niobium deposited on sapphire and SiO<sub>2</sub>/Si substrates. The samples have been characterized at temperatures down to 30 mK. In this work we discuss two important properties of these resonators: The tunability of the centre frequency using a weak applied magnetic field, and the RF-power dependence of the quality factor

Numerical simulations of a flux qubit coupled to a high quality resonator

Circuit-QED - the electrical analogue of cavity quantum electrodynamics in atomic physics - is an emerging field of research. By coupling superconducting qubits to an on-chip high-quality resonator it is possible to study a number of effects that are of interest for fundamental tests of quantum mechanics and also have potential applications in quantum information processing, metrology and communication. We have performed computer simulations of a system comprising a flux qubit strongly coupled to a high-quality coplanar waveguide resonator driven by an external microwave source. Using realistic values for the various parameters we have studied, among other things, the transmittance of the cavity and the spectrum of the emitted radiation