Search results for "Classical physics"
showing 10 items of 190 documents
Quantum Criticality in a Bosonic Josephson Junction
2011
In this paper we consider a bosonic Josephson junction described by a two-mode Bose-Hubbard model, and we thoroughly analyze a quantum phase transition occurring in the system in the limit of infinite bosonic population. We discuss the relation between this quantum phase transition and the dynamical bifurcation occurring in the spectrum of the Discrete Self Trapping equations describing the system at the semiclassical level. In particular, we identify five regimes depending on the strength of the effective interaction among bosons, and study the finite-size effects arising from the finiteness of the bosonic population. We devote a special attention to the critical regime which reduces to th…
Dynamical bifurcation as a semiclassical counterpart of a quantum phase transition
2011
We illustrate how dynamical transitions in nonlinear semiclassical models can be recognized as phase transitions in the corresponding -- inherently linear -- quantum model, where, in a Statistical Mechanics framework, the thermodynamic limit is realized by letting the particle population go to infinity at fixed size. We focus on lattice bosons described by the Bose-Hubbard (BH) model and Discrete Self-Trapping (DST) equations at the quantum and semiclassical level, respectively. After showing that the gaussianity of the quantum ground states is broken at the phase transition, we evaluate finite populations effects introducing a suitable scaling hypothesis; we work out the exact value of the…
Assessment of the Reliability of the SPAC Method in Urban Areas
2015
We have carried out several long-term measures of seismic noise with triangular arrays of broad-band seismic sensors, to investigate the reliability of the SPAC method in urban areas. We investigate the stationary and anisotropy of the microtremor wave field. We have found that the anisotropy of the microtremor wave field can be evaluated analyzing the HVNSR as function the azimuth. Furthermore, we showed as strong anisotropies in the microtremors are often observable in particular at high frequencies (> 1 Hz). We have verified as microtremors can be difficult to considered as ergodic processes, and for this reason time averaging, also even over a long periods of time, cannot replace an app…
Quantum Probes for the Characterization of Nonlinear Media
2021
Active optical media leading to interaction Hamiltonians of the form H=λ˜(a+a†)ζ represent a crucial resource for quantum optical technology. In this paper, we address the characterization of those nonlinear media using quantum probes, as opposed to semiclassical ones. In particular, we investigate how squeezed probes may improve individual and joint estimation of the nonlinear coupling λ˜ and of the nonlinearity order ζ. Upon using tools from quantum estimation, we show that: (i) the two parameters are compatible, i.e., the may be jointly estimated without additional quantum noise
On the history of torsional stress concentrations in shafts: From electrical analogies to numerical methods
2014
This article proposes a retrospective on experimental and numerical methods developed throughout the past century to solve the torsion problem in shafts, with particular emphasis on the determination of shear stress concentration factors in discontinuities of typical use in shaft design. This article, in particular, presents the theory and related solutions distinguishing between two classes of geometries: shafts with constant cross section and axisymmetric shafts with variable diameter. Emphasis is given to approaches based on physical analog methods and, in particular, those based on electrical analogies proposed since about 1925. Experimental methods based on structural physical models …
Cloaking In-Plane Elastic Waves with Swiss Rolls
2020
We propose a design of cylindrical cloak for coupled in-plane shear waves consisting of concentric layers of sub-wavelength resonant stress-free inclusions shaped as Swiss rolls. The scaling factor between inclusions&rsquo
Numerical study of the Kadomtsev–Petviashvili equation and dispersive shock waves
2018
A detailed numerical study of the long time behaviour of dispersive shock waves in solutions to the Kadomtsev-Petviashvili (KP) I equation is presented. It is shown that modulated lump solutions emerge from the dispersive shock waves. For the description of dispersive shock waves, Whitham modulation equations for KP are obtained. It is shown that the modulation equations near the soliton line are hyperbolic for the KPII equation while they are elliptic for the KPI equation leading to a focusing effect and the formation of lumps. Such a behaviour is similar to the appearance of breathers for the focusing nonlinear Schrodinger equation in the semiclassical limit.
Optical retarder system with programmable spectral retardance.
2014
An optical system that works as a retarder waveplate with programmable spectral retardance is proposed. The system is based on a pixelated liquid crystal on silicon (LCoS) spatial light modulator (SLM). The input light beam is spectrally dispersed and different spectral components are projected onto different pixels of the LCoS-SLM. A different retardance is then addressed for each pixel, adapted to the incoming wavelength. Light reflected from the SLM is then recombined by the same setup. In this way a programmable polarization spectrum can be encoded. We illustrate the broadband characterization that is required for proper use of the system. Then several examples are shown, including spec…
Saturated absorption spectroscopy: elimination of crossover resonances by use of a nanocell
2007
It is demonstrated that velocity selective optical pumping/saturation resonances of reduced absorption in a Rb vapor nanocell with thickness \textit{L=} $\lambda $, 2$\lambda $, and 3$\lambda $ (resonant wavelength $\lambda $ = 780 nm) allow the complete elimination of crossover (CO) resonances. We observe well pronounced resonances corresponding to the F$_{g}=3$ $\to $ F$_{e}=2,3,4$ hyperfine transitions of the $^{85}$Rb D$_{2}$ line with linewidths close to the natural width. A small CO resonance located midway between F$_{g}=3$ $\to $ F$_{e}=3$ and F$_{g}=3$ $\to$ F$_{e}=4$ transitions appears only for \textit{L} = 4$\lambda $. The D$_{2}$ line ($\lambda $ = 852 nm) in a Cs nanocell exhi…
Numerical simulation of creeping fluid flow in reconstruction models of porous media
2002
Abstract In this paper we examine representative examples of realistic three-dimensional models for porous media by comparing their geometry and permeability with those of the original experimental specimen. The comparison is based on numerically exact evaluations of permeability, porosity, specific internal surface, mean curvature, Euler number and local percolation probabilities. The experimental specimen is a three-dimensional computer tomographic image of Fontainebleau sandstone. The three models are stochastic reconstructions for which many of the geometrical characteristics coincide with those of the experimental specimen. We find that in spite of the similarity in the geometrical pro…