arXiv subjects

A. A. Lisboa de Souza

Publications and source records attributed to A. A. Lisboa de Souza.

5 recordsLinked to original sources

arXiv2026

Deep squeezing or cooling the fluctuations of a parametric resonator using feedback

Here we analyze ways to achieve deep subthreshold parametric squeezing or cooling of a single degree-of-freedom parametric resonator enhanced by a lock-in amplifier feedback loop. Due to the feedback, the dynamics of the parametric resonator becomes more complex and a Hopf bifurcation at the instability threshold can occur. Initially, we calculate the phase-dependent gain of parametric amplification with feedback of an added ac signal. In one approach, we obtain the amplification gain approximately using two independent approaches: the averaging method and the harmonic balance method. We also obtain this gain more exactly using Floquet theory and Green's functions methods. The Hopf bifurcation was predicted by the harmonic balance method and by Floquet theory, but not by the averaging method. In our analysis of fluctuations, we Fourier analyze the response of the parametric resonator with feedback to an added white noise. We were able to calculate, in addition to the noise spectral density, the squeezing of fluctuations in this resonator with feedback. Very strong squeezing or cooling can occur. Deamplification and cooling occur near the Hopf bifurcation, whereas squeezing occurs near a saddle-node bifurcation.

quant-ph↗

arXiv2024

Deep noise squeezing in parametrically driven resonators

Here we investigate white noise squeezing in the frequency domain of classical parametrically-driven resonators with added noise. We use Green's functions to analyse the response of resonators to added noise. In one approach, we obtain the Green's function approximately using the first-order averaging method, while in the second approach, exactly, using Floquet theory. We characterize the noise squeezing by calculating the statistical properties of the real and imaginary parts of the Fourier transform of the resonators response to added noise. In a single parametric resonator, due to correlation, the squeezing limit of $-6$~dB can be reached even with detuning at the instability threshold in a single parametrically-driven resonator. We also applied our techniques to investigate squeezing in a dynamical system consisting a parametric resonator linearly coupled to a harmonic resonator. In this system, we were able to observe deep squeezing at around $-40$~dB in one of the quadratures of the harmonic resonator response. We noticed that this occurs near a Hopf bifurcation to parametric instability, which is only possible when the dynamics of the coupled resonators cannot be decomposed into normal modes. Finally, we also showed that our analysis of squeezing based on Floquet theory can be applied to multiple coupled resonators with parametric modulation and multiple noise inputs.

physics.app-ph↗

arXiv2021

Stochastic resonance and amplification in the ac driven Duffing oscillator with added noise

Stochastic resonance (SR) is a coherence enhancement effect due to noise that occurs in periodically-driven nonlinear dynamical systems. A very broad range of physical and biological systems present this effect such as climate change, neurons, neural networks, lasers, SQUIDS, and tunnel diodes, among many others. Early theoretical models of SR dealt only with overdamped bistable oscillators. Here, we propose a simple model that accounts for SR in an underdamped driven Duffing oscillator with added white noise. Furthermore, we develop a theoretical method to predict the effect of white noise on the pump, signal, and idler responses of a Duffing amplifier. We also calculate the power spectral density of the response of the Duffing amplifier. This approach may prove to be useful for assessing the robustness of acoustic, phononic, or mechanical frequency-comb generation to the presence of noise.

nlin.PS↗

arXiv2020

Frequency-comb response of a parametrically-driven Duffing oscillator to a small added ac excitation

Here we present a one-degree-of-freedom model of a nonlinear parametrically-driven resonator in the presence of a small added ac signal that has spectral responses similar to a frequency comb. The proposed nonlinear resonator has a spread spectrum response with a series of narrow peaks that are equally spaced in frequency. The system displays this behavior most strongly after a symmetry-breaking bifurcation at the onset of parametric instability. We further show that the added ac signal can suppress the transition to parametric instability in the nonlinear oscillator. We also show that the averaging method is able to capture the essential dynamics involved.

nlin.PS↗

arXiv2015

Gain and noise spectral density in an electronic parametric amplifier with added white noise

In this paper, we discuss the behavior of a linear classical parametric amplifier (PA) in the presence of white noise and give theoretical estimates of the noise spectral density based on approximate Green's functions obtained by using averaging techniques. Furthermore, we give analytical estimates for parametric amplification bandwidth of the amplifier and for the noisy precursors to instability. To validate our theory we compare the analytical results with experimental data obtained in an analog circuit. We describe the implementation details and the setup used in the experimental study of the amplifier. Near the threshold to the first parametric instability, and in degenerate-mode amplification, the PA achieved very high gains in a very narrow bandwidth centered on its resonance frequency. In quasi-degenerate mode amplification, we obtained lower values of gain, but with a wider bandwidth that is tunable. The experimental data were accurately described by the predictions of the model. Moreover, we noticed spectral components in the output signal of the amplifier which are due to noise precursors of instability. The position, width, and magnitude of these components are in agreement with the noise spectral density obtained by the theory proposed here.

physics.class-ph↗