Interface free energy or surface tension: definition and basic properties

Interface free energy is the contribution to the free energy of a system due to the presence of an interface separating two coexisting phases at equilibrium. It is also called surface tension. The content of the paper is 1) the definition of the interface free energy from first principles of statistical mechanics; 2) a detailed exposition of its basic properties. We consider lattice models with short range interactions, like the Ising model. A nice feature of lattice models is that the interface free energy is anisotropic so that some results are pertinent to the case of a crystal in equilibrium with its vapor. The results of section 2 hold in full generality.Comment: 20 pages, 2 figure

Interface Pinning and Finite-Size Effects in the 2D Ising Model

We apply new techniques developed in a previous paper to the study of some surface effects in the 2D Ising model. We examine in particular the pinning-depinning transition. The results are valid for all subcritical temperatures. By duality we obtained new finite size effects on the asymptotic behaviour of the two-point correlation function above the critical temperature. The key-point of the analysis is to obtain good concentration properties of the measure defined on the random lines giving the high-temperature representation of the two-point correlation function, as a consequence of the sharp triangle inequality: let tau(x) be the surface tension of an interface perpendicular to x; then for any x,y tau(x)+tau(y)-tau(x+y) >= 1/kappa(||x||+||y||-||x+y||), where kappa is the maximum curvature of the Wulff shape and ||x|| the Euclidean norm of x.Comment: 34 pages, Late

Non-Analyticity and the van der Waals Limit

We study the analyticity properties of the free energy f_\ga(m) of the Kac model at points of first order phase transition, in the van der Waals limit \ga\searrow 0. We show that there exists an inverse temperature $\beta_0$ and \ga_0>0 such that for all $\beta\geq \beta_0$ and for all \ga\in(0,\ga_0), f_\ga(m) has no analytic continuation along the path $m\searrow m^*$ ($m^*$ denotes spontaneous magnetization). The proof consists in studying high order derivatives of the pressure p_\ga(h), which is related to the free energy f_\ga(m) by a Legendre transform

The Challenges of the "New Economy" for Monetary Policy

The advent and spread of information and communication technologies (ICTs) increase potential output growth . It is uncertain to what extent and for how long they do so. We use the term "new economy" (NE) to describe the acceleration in potential output growth and the attendant and partly temporary slowdown in inflation. Assessing the NE is however a complicated and delicate task. The impact of the NE on the conduct of monetary policy may differ depending on the time scale. In a long-run perspective, the central bank could capitalise on the NE to set lower inflation targets. In the short to medium term, central banks should be cautious when identifying changing patterns in potential output growth, as temporary errors in appreciation may have an asymmetrical impact on economic stability: the production instability that could result from central banks mistakenly perceiving the advent of a NE would be greater than that generated by the failure to recognise a genuine rise in potential output growth.Monetary policy ; Productivity ; New economy ; Uncertainty ; Measurement issues.

Observation of triply coincident nonlinearities in periodically poled KTiOPO4

We report the simultaneous quasi-phase-matching of all three possible nonlinearities for propagation along the X axis of periodocally poled (PP) KTiOPO4 (KTP) for second-harmonic generation of 745 nm pulsed light from 1490nm subpicosecond pulses in a PPKTP crystal with a 45.65 micrometer poling period. This confirms the recent Sellmeier fits of KTP by K. Kato and E. Takaoka [Appl. Opt. 41, 5040 (2002)]. Such coincident nonlinearities are of importance for realizing compact sources of multipartite continuous-variable entanglement [Pfister et al., Phys. Rev. A 70, 020302 (2004)] and we propose a new simpler method for entangling four fields, based on this triple coincidence.Comment: 3 pages, 4 figures, submitted for publicatio

Stratospheric pollutant transports by planetary waves and tropical circulations

Radiosonde and U-2 aircraft data from the Intertropical Convergence Zone experiment of July, 1977 were analyzed. The radiosonde data above 15 km was plotted in the form of time-height sections so that wave motions in the meteorological variables (temperature, zonal wind, and meridional wind) could be easily delineated. The results showed the presence of a planetary 16 day Kelvin wave. More significantly, large amplitude gravity waves with vertical wavelengths on the order of 3-6 km were found. Spectral analysis of frequencies showed peaks in meridional wind variance at 2-3 days and 5 days, with the shorter periods stronger at higher altitudes. In the time domain, two instances of organized wave groups propagating upward into the stratosphere were isolated. Associated with one of these wave groups was a region of very large vertical shear in which either turbulence or small scale (10 km wavelength or less) gravity wave activity had been found by the U-2 aircraft

Experimental realization of multipartite entanglement of 60 modes of a quantum optical frequency comb

We report the experimental realization and characterization of one 60-mode copy, and of two 30-mode copies, of a dual-rail quantum-wire cluster state in the quantum optical frequency comb of a bimodally pumped optical parametric oscillator. This is the largest entangled system ever created whose subsystems are all available simultaneously. The entanglement proceeds from the coherent concatenation of a multitude of EPR pairs by a single beam splitter, a procedure which is also a building block for the realization of hypercubic-lattice cluster states for universal quantum computing.Comment: Accepted by PRL. 5 pages, 5 figures + 14 pages, 9 figures of supplemental material. Ver3: better experimental dat

The Optical Frequency Comb as a One-Way Quantum Computer

In the one-way model of quantum computing, quantum algorithms are implemented using only measurements on an entangled initial state. Much of the hard work is done up-front when creating this universal resource, known as a cluster state, on which the measurements are made. Here we detail a new proposal for a scalable method of creating cluster states using only a single multimode optical parametric oscillator (OPO). The method generates a continuous-variable cluster state that is universal for quantum computation and encoded in the quadratures of the optical frequency comb of the OPO. This work expands on the presentation in Phys. Rev. Lett. 101, 130501 (2008).Comment: 20 pages, 8 figures. v2 corrects minor error in published versio