A Microwave Josephson Refrigerator

We present a microwave quantum refrigeration principle based on the Josephson effect. When a superconducting quantum interference device (SQUID) is pierced by a time-dependent magnetic flux, it induces changes in the macroscopic quantum phase and an effective finite bias voltage appears across the SQUID. This voltage can be used to actively cool well below the lattice temperature one of the superconducting electrodes forming the interferometer. The achievable cooling performance combined with the simplicity and scalability intrinsic to the structure pave the way to a number of applications in quantum technology.Comment: 6 pages, 3 figure

Radiation comb generation with extended Josephson junctions

We propose the implementation of a Josephson radiation comb generator (JRCG) based on an extended Josephson junction subject to a time dependent magnetic field. The junction critical current shows known diffraction patterns and determines the position of the critical nodes when it vanishes. When the magnetic flux passes through one of such critical nodes, the superconducting phase must undergo a $\pi$-jump to minimize the Josephson energy. Correspondingly a voltage pulse is generated at the extremes of the junction. Under periodic driving this allows us to produce a comb-like voltage pulses sequence. In the frequency domain it is possible to generate up to hundreds of harmonics of the fundamental driving frequency, thus mimicking the frequency comb used in optics and metrology. We discuss several implementations through a rectangular, cylindrical and annular junction geometries, allowing us to generate different radiation spectra and to produce an output power up to $10$~pW at $50$~GHz for a driving frequency of $100$~MHz.Comment: 4+ pages, 4 color figure

Parasitic effects in SQUID-based radiation comb generators

We study several parasitic effects on the implementation of a Josephson radiation comb generator (JRCG) based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. This system can be used as a radiation generator similarly to what is done in optics and metrology, and allows one to generate up to several hundreds of harmonics of the driving frequency. First we take into account how assuming a finite loop geometrical inductance and junction capacitance in each SQUID may alter the operation of this device. Then, we estimate the effect of imperfections in the fabrication of an array of SQUIDs, which is an unavoidable source of errors in practical situations. We show that the role of the junction capacitance is in general negligible, whereas the geometrical inductance has a beneficial effect on the performance of the device. The errors on the areas and junction resistance asymmetries may deteriorate the performance, but their effect can be limited up to a large extent with a suitable choice of fabrication parameters.Comment: 9 pages, 9 figure

Gate-modulated thermopower in disordered nanowires: I. Low temperature coherent regime

Using a one-dimensional tight-binding Anderson model, we study a disordered nanowire in the presence of an external gate which can be used for depleting its carrier density (field effect transistor device configuration). In this first paper, we consider the low temperature coherent regime where the electron transmission through the nanowire remains elastic. In the limit where the nanowire length exceeds the electron localization length, we derive three analytical expressions for the typical value of the thermopower as a function of the gate potential, in the cases where the electron transport takes place (i) inside the impurity band of the nanowire, (ii) around its band edges and eventually (iii) outside its band. We obtain a very large enhancement of the typical thermopower at the band edges, while the sample to sample fluctuations around the typical value exhibit a sharp crossover from a Lorentzian distribution inside the impurity band towards a Gaussian distribution as the band edges are approached.Comment: 13 pages, 8 figures, final version as publishe

Photonic heat conduction in Josephson-coupled Bardeen-Cooper-Schrieffer superconductors

We investigate the photon-mediated heat flow between two Josephson-coupled Bardeen-Cooper-Schrieffer (BCS) superconductors. We demonstrate that in standard low temperature experiments involving temperature-biased superconducting quantum interference devices (SQUIDs), this radiative contribution is negligible if compared to the direct galvanic one, but it largely exceeds the heat exchanged between electrons and the lattice phonons. The corresponding thermal conductance is found to be several orders of magnitude smaller, for real experiments setup parameters, than the universal quantum of thermal conductance, kappa_0(T)=pi k_B^2T/6hbar.Comment: 8 pages, 6 figure

Absorbing/Emitting Phonons with one dimensional MOSFETs

We consider nanowires in the field effect transistor device configuration. Modeling each nanowire as a one dimensional lattice with random site potentials, we study the heat exchanges between the nanowire electrons and the substrate phonons, when electron transport is due to phonon-assisted hops between localized states. Shifting the nanowire conduction band with a metallic gate induces different behaviors. When the Fermi potential is located near the band center, a bias voltage gives rise to small local heat exchanges which fluctuate randomly along the nanowire. When it is located near one of the band edges, the bias voltage yields heat currents which flow mainly from the substrate towards the nanowire near one boundary of the nanowire, and in the opposite direction near the other boundary. This opens interesting perspectives for heat management at submicron scales: Arrays of parallel gated nanowires could be used for a field control of phonon emission/absorption.Comment: 9 pages, 11 figure

Considérations didactiques autour du répertoire (pluri) linguistique de l’apprenant : du CARAP à la classe de langue

La prise en compte des caractéristiques d'une société de plus en plus multilingue et, par conséquent, du patrimoine (pluri)linguistique et pluriculturel des individus est désormais indispensable, surtout dans le système éducatif et notamment dans la formation de tous les enseignants, ceux qui enseignent les langues et ceux qui enseignent en langue (maternelle, seconde ou étrangère). Cet article propose quelques réflexions pour la mise en place d'une didactique à visées plurilingue et interculturelle à partir des recommandations nationales et européennes les plus récentes et tout spécialement des indications du Cadre de référence pour les approches plurielles (CARAP)

vocoids and their prosodic distribution, with special reference to Italian and Arabic

This study attempts to characterize vocoids, i.e. vowels and semivowels, as a unified class of segments. In order to do so, it investigates the main phenomena concerning the quantitative distribution of these sounds, namely syllabic alternation, length alternations, deletion and insertion. Such phenomena are best analyzed by making reference to prosodic structure, and syllable structure in particular. Therefore, both frameworks adopted in this thesis take into consideration this type of representation. The main approach, which I refer to generally as Derivational Theory (DT), is based on the notion that surface phonetic forms are derived from underlying forms through a series of structural changes taking place at different levels of representation. This model is contrasted with the recently introduced (Prince and Smolensky 1993) Optimality Theory (OT), an output-oriented paradigm based on the parallel evaluation of candidate forms by means of universal but violable constraints. This thesis shows that OT offers some valuable insights into the phenomena under analysis, although there are areas in which it requires integration with derivational tools. This study also makes specific reference to two languages: Ammani Arabic and Standard Italian. These diverge in their treatment of vocoids, but clear general trends may be detected which have also been found in other languages