Noise-Free Measurement of Harmonic Oscillators with Instantaneous Interactions

We present a method of measuring the quantum state of a harmonic oscillator through instantaneous probe-system selective interactions of the Jaynes-Cummings type. We prove that this scheme is robust to general decoherence mechanisms, allowing the possibility of measuring fast-decaying systems in the weak-coupling regime. This method could be applied to different setups: motional states of trapped ions, microwave fields in cavity/circuit QED, and even intra-cavity optical fields.Comment: 4 pages, no figure, published in Physical Review Letter

Cν\nuB damping of primordial gravitational waves and the fine-tuning of the Cγ\gammaB temperature anisotropy

Damping of primordial gravitational waves due to the anisotropic stress contribution owing to the cosmological neutrino background (C$\nu$B) is investigated in the context of a radiation-to-matter dominated Universe. Besides its inherent effects on the gravitational wave propagation, the inclusion of the C$\nu$B anisotropic stress into the dynamical equations also affects the tensor mode contribution to the anisotropy of the cosmological microwave background (C$\gamma$B) temperature. Given that the fluctuations of the C$\nu$B temperature in the (ultra)relativistic regime are driven by a multipole expansion, the mutual effects on the gravitational waves and on the C$\gamma$B are obtained through a unified prescription for a radiation-to-matter dominated scenario. The results are confronted with some preliminary results for the radiation dominated scenario. Both scenarios are supported by a simplified analytical framework, in terms of a scale independent dynamical variable, $k \eta$, that relates cosmological scales, $k$, and the conformal time, $\eta$. The background relativistic (hot dark) matter essentially works as an effective dispersive medium for the gravitational waves such that the damping effect is intensified for the Universe evolving to the matter dominated era. Changes on the temperature variance owing to the inclusion of neutrino collision terms into the dynamical equations result into spectral features that ratify that the multipole expansion coefficients $C_{l}^{T}$'s die out for $l \sim 100$.Comment: 24 pages, 8 figure

Non-equilibrium tube length fluctuations of entangled polymers

We investigate the nonequilibrium tube length fluctuations during the relaxation of an initially stretched, entangled polymer chain. The time-dependent variance $\sigma^2$ of the tube length follows in the early-time regime a simple universal power law $\sigma^2 = A \sqrt{t}$ originating in the diffusive motion of the polymer segments. The amplitude $A$ is calculated analytically both from standard reptation theory and from an exactly solvable lattice gas model for reptation and its dependence on the initial and equilibrium tube length respectively is discussed. The non-universality suggests the measurement of the fluctuations (e.g. using flourescence microscopy) as a test for reptation models.Comment: 12 pages, 2 figures. Minor typos correcte

Magnetism of Substitutional Co Impurities in Graphene: Realization of Single π\pi-Vacancies

We report {\it ab initio} calculations of the structural, electronic and magnetic properties of a graphene monolayer substitutionally doped with Co (Co$_{sub}$) atoms. We focus in Co because among traditional ferromagnetic elements (Fe, Co and Ni), only Co$_{sub}$ atoms induce spin-polarization in graphene. Our results show the complex magnetism of Co substitutional impurites in graphene, which is mapped into simple models such as the $\pi$-vacancy and Heisenberg model. The links established in our work can be used to bring into contact the engineering of nanostructures with the results of $\pi$-models in defective graphene. In principle, the structures considered here can be fabricated using electron irradiation or Ar$^+$ ion bombardment to create defects and depositing Co at the same time

Evidence for an inflationary phase transition from the LSS and CMB anisotropy data

In the light of the recent Boomerang and Maxima observations of the CMB which show an anomalously low second acoustic peak, we reexamine the prediction by Adams et al (1997) that this would be the consequence of a 'step' in the primordial spectrum induced by a spontaneous symmetry breaking phase transition during primordial inflation. We demonstrate that a deviation from scale-invariance around $k\sim0.1h$~Mpc$^{-1}$ can simultaneously explain both the feature identified earlier in the APM galaxy power spectrum as well the recent CMB anisotropy data, with a baryon density consistent with the BBN value. Such a break also allows a good fit to the data on cluster abundances even for a critical density matter-dominated universe with zero cosmological constant.Comment: 4 pages with 3 figures, LaTeX file using espcrc2.sty to appear on the Proceedings of "Euroconference on Frontiers in Particle Astrophysics and Cosmology",Sant Feliu de Guixols,Spain,30th September-5th October of 200