arXiv subjects

Giorgio Fontana

Publications and source records attributed to Giorgio Fontana.

12 recordsLinked to original sources

arXiv2019

Time response of a microring resonator to a rectangular pulse in different coupling regimes

We discuss the analytical temporal response of a microring resonator excited through a bus waveguide by an optical rectangular pulse. Finite difference time domain (FDTD) simulations illustrate the analytical solution and help in understanding the meaning of the different coupling regimes. In addition, we show that the temporal dynamics allows determing the coupling regime while the commonly used spectral characterization in the stationary regime does not. We also take advantage of the simulation to highlight the phase shift between the input and the output signals in the different coupling regimes. Finally, measurements on a Si3N4 microring resonator are performed and analyzed in the case of under-coupling regime to illustrate how the time response study leads to the Q-factor determination.

physics.optics↗

arXiv2009

Gravitational waves in the Hyperspace?

In the framework of the debate on high-frequency gravitational waves (GWs), after a review of GWs in standard General Relativity, which is due for completness, the possibility of merging such a traditional analysis with the Hyperspace formalism that has been recently introduced in some papers in the literature, with the goal of a better understanding of manifolds dimensionality also in a cosmological framework, is discussed. Using the concept of refractive index in the Hyperspace, spherical solutions are given and the propagation of GWs in a region of the Hyperspace with an unitary refractive index is also discussed. Propagation phenomena associated to the higher dimensionality are proposed, possibly including non-linear effects. Further and accurate studies in this direction are needed.

astro-ph.CO↗

arXiv2006

Why we live in the Computational Universe

To better understand the deep significance of our best physical theories it could be interesting to compare our Universe with its models. It may happen that the differences between the model and reality can be made indistinguishable, to the point that it may seem acceptable to consider reality as a gigantic program, a 'mother computation' running in a Universal Computer. The computational interpretation of reality is here adopted for introducing concepts that are common in computer science, they may offer a new insight. For instance, code and memory usage optimization techniques are common in computer science because they improve the performances at a reduced hardware cost. According to the concepts discussed in this paper, the possibility of recognizing the effects of optimization rules in a physical reality will allow us to discriminate if our reality is fundamental or the result of a large computation. Conversely, code and memory optimization has side effects, if it is present in our Universe it can produce many interesting phenomena, some seem readily recognizable, others only wait to be discovered.

physics.gen-ph↗

arXiv2004

The Four Space-times Model of Reality

We live in a 3+1 space-time that is intended as a description of the universe with three space dimensions and one time dimension. Space-time dimensionality seems so natural that it is rarely criticized. Experiments and the highly successful relativistic theories teach us that there are four fundamental dimensions, among them is time that is treated as a special dimension. The specialty of time can be removed, leading to the concept that time is simply a function of four new fundamental dimensions, which have now identical properties, in combination with Lorentz invariance. A model is deduced in which a 4-space, characterized by four space-like coordinates, may host four "equivalent but orthogonal" space-times, each with three spatial coordinates and one temporal coordinate. Coordinates are shared; therefore the 4-space and the four space-times are all in one. Electromagnetic interaction is confined in each space-time and the role of the speed of light appears to be that of a barrier for the electromagnetic interaction. The motion of objects can be described by four-dimensional optics in the 4-space. Each of the four space-times may host a universe and, in agreement with recent observations, the proposed model can be directly applied to problems like the cosmological matter-antimatter asymmetry and dark-matter issues. Space travel may also benefit from the concepts presented.

physics.gen-ph↗

arXiv2004

Design of a Quantum Source of High-Frequency Gravitational Waves (HFGW) and Test Methodology

The generation of High-Frequency Gravitational Waves (HFGW) has been identified as the required breakthrough that will lead to new forms of space propulsion. Many techniques have been devised to generate HFGW, but most of them exhibit marginal efficiency, therefore the power emitted in form of gravitational waves (GW) is orders of magnitude lower than the input power. The gravitational wave counterpart of the LASER, termed Gravitational-wave LASER or "GASER" is the quantum approach to the efficient generation of gravitational waves. Electrons, protons, muons, etc, all have charge and mass, if accelerated they usually lose energy through the very fast electric and magnetic channels, this causes a negligible emission through the gravitational channel. Quantum systems can be engineered to forbid electric and magnetic transitions, therefore the gravitational spin-2 transitions can take place. A class of active materials, suitable for making a GASER based on electronic transitions in the solid state, is identified along with their relevant physical properties. Means for creating coherence and population inversion and means to increase the emission probability are described. The expected performances of the device are derived from quantum gravitational theories. Additional properties of the active materials are considered to enforce the theoretical foundation of the device. A proof-of-concept device, operating at about 1 THz, is described. Experiments are proposed as a natural starting point of the research.

physics.gen-ph↗

arXiv2004

Effect of the Vacuum Energy Density on Graviton Propagation

It is known that the value L of the vacuum energy density affects the propagation equation for gravitons: A mass term appears in the propagation equation, such that m^2=-L. As a consequence, the polarization states of gravitons also change. This effect of the L-term has been confirmed by recent calculations in a curved background, which is the only proper setting, since solutions of the classical Einstein equations in the presence of a L-term represent a space with constant curvature. A real value for the mass (when L<0) will show up as a slight exponential damping in the gravitational potential, which is however strongly constrained by astronomical data. The consequences of an imaginary mass (for L>0) are still unclear; on general grounds, one can expect the onset of instabilities in this case. This is also confirmed by numerical simulations of quantum gravity which became recently available. These properties gain a special interest in consideration of the following. (1) The most recent cosmological data indicate that L is positive and of the order of 0.1 J/m^3. Is this value compatible with a stable propagation of gravitons? (2) The answer to the previous question lies perhaps in the scale dependence of the effective value of L. L may be negative at the small distance/large energy scale at which the quantum behavior of gravitational fields and waves becomes relevant. Furthermore, local contributions to the vacuum energy density (in superconductors in certain states, and in very strong static electromagnetic fields) can change locally the sign of L, and so affect locally the propagation and the properties of gravitons. The graviton wavefunction, for different values of the parameters, may be characterized by superluminal phase velocity or by unitarity only in imaginary valued time.

physics.gen-ph↗

arXiv2003

Compensated Current Injection circuit, theory and applications

This paper presents a detailed description, analysis and example of practical application of a wide frequency band voltage-to-current converter. The converter is characterized by a combination of positive and negative feedback loops. This feature allows compensation for parasitic impedance connected in parallel with the useful load, which in turn keeps an excitation current flowing through the useful load independent of its impedance. The simplicity of the circuit and its good electrical properties are additional advantages of the scheme.

physics.ins-det↗

arXiv2002

Possible Graviton Transitions and Gaser Action in High-Tc Superconductors

It is well known that excited quantum systems can emit gravitons as well as photons. Differently from photon emission, spontaneous graviton emission is characterized by such a low probability that stimulated emission appears the only possible mechanism for producing gravitational radiation with quantum systems. The principles of the gravitational counterpart of the laser, which has been named gaser, have been theorized decades ago. Now a class of high temperature superconductors might be identified as a viable active material for practical gaser action.

cond-mat.supr-con↗

arXiv2002

High Performance Electrostatic Sensors and Actuators for LISA Proof Mass Control

This document contains two presentations which describe the working principles of a class of electrostatic multidimensional sensors and force actuators. The subject of the study is the search of the most effective methods for measuring the position of a cubical conducting proof mass which floats in a weightless environment. The same proof mass must be controlled with a feedback loop by applying forces with the same set of electrodes. For more information please see the web site: http://lisa.jpl.nasa.gov/

physics.ins-det↗

arXiv2001

Gravitational Radiation and its Application to Space Travel, principles and required scientific developments

Gravitational radiation is an elusive form of radiation predicted by general relativity, it is the subject of intense theoretical and experimental research at the limit of the sensitivity of today's instrumentation. In spite of the fact that no direct evidence of this radiation now exist, observed astrophysical phenomena have given convincing proofs of its existence. Theories predict that gravitational radiation may also be employed for propulsion, moreover the nonlinear behaviour of spacetime may permit the generation of spacetime singularities with colliding beams of gravitational radiation, this phenomenon could become a form of propellantless propulsion. Both applications would require gravitational wave generators with high power and appropriate optical properties. Among the proposed techniques that could be applicable to the production of gravitational waves, a promising one is the possible emission of gravitons by quantum systems. A hypothesis describing the production of gravitons in s-wave/d-wave superconductor junction is presented.

physics.space-ph↗

arXiv1998

A possibility of emission of high frequency gravitational radiation from junctions between d-wave and s-wave superconductors

Recent measurements on a class of high-Tc superconductors (HTSCs) have shown that Cooper-pairs wavefunction is a d-wave, while in another class, d-wave and s-wave may coexist. Conventional low-Tc superconductors are s-wave superconductors. When d-wave Cooper-pairs are injected in a superconductor that can sustain s-wave pairing, d-wave pairs are subject to transition to s-wave pairs and energy is irradiated by means of gravitons. We show that in s-wave to d-wave type superconductor (SDS) junctions in an equilibrium condition no net gravitational wave energy is emitted, on the other hand under non equilibrium conditions a net gravitational wave energy is emitted by the junction. Experiments that show a gravitational interaction between inhomogeneous high-Tc superconductors, under non-equilibrium conditions, and test objects may be understood by accepting a possibility of emission of gravitational radiation from SDS junctions.

cond-mat.supr-con↗

arXiv1998

A possibility of emission of high frequency gravitational radiation from d-wave to s-wave type superconductor junctions

Recent measurements on a class of high-Tc superconductors (HTSC) have shown that Cooper-pairs binding may be associated to a d-wave, while in another class, d and s waves may coexist. When d-wave Cooper-pairs are injected in a superconductor that can sustain s-wave binding, d-wave pairs decay to s-wave pairs and energy is irradiated by means of gravitons. We show that in s-wave to d-wave type superconductor (SDS) junctions in an equilibrium condition no net gravitational wave energy is emitted, on the other hand under non equilibrium conditions a net gravitational wave energy is emitted by the junction. Experiments which show a gravitational interaction between inomogeneus high-Tc superconductors, under non equilibrium conditions, and test objects may be understood by accepting a possibility of emission of gravitational radiation from SDS junctions.

gr-qc↗