1,036 research outputs found
Inhomogeneous mechanical losses in micro-oscillators with high reflectivity coating
We characterize the mechanical quality factor of micro-oscillators covered by
a highly reflective coating. We test an approach to the reduction of mechanical
losses, that consists in limiting the size of the coated area to reduce the
strain and the consequent energy loss in this highly dissipative component.
Moreover, a mechanical isolation stage is incorporated in the device. The
results are discussed on the basis of an analysis of homogeneous and
non-homogeneous losses in the device and validated by a set of Finite-Element
models. The contributions of thermoelastic dissipation and coating losses are
separated and the measured quality factors are found in agreement with the
calculated values, while the absence of unmodeled losses confirms that the
isolation element integrated in the device efficiently uncouples the dynamics
of the mirror from the support system. Also the resonant frequencies evaluated
by Finite-Element models are in good agreement with the experimental data, and
allow the estimation of the Young modulus of the coating. The models that we
have developed and validated are important for the design of oscillating
micro-mirrors with high quality factor and, consequently, low thermal noise.
Such devices are useful in general for high sensitivity sensors, and in
particular for experiments of quantum opto-mechanics
Detection of weak stochastic force in a parametrically stabilized micro opto-mechanical system
Measuring a weak force is an important task for micro-mechanical systems,
both when using devices as sensitive detectors and, particularly, in
experiments of quantum mechanics. The optimal strategy for resolving a weak
stochastic signal force on a huge background (typically given by thermal noise)
is a crucial and debated topic, and the stability of the mechanical resonance
is a further, related critical issue. We introduce and analyze the parametric
control of the optical spring, that allows to stabilize the resonance and
provides a phase reference for the oscillator motion, yet conserving a free
evolution in one quadrature of the phase space. We also study quantitatively
the characteristics of our micro opto-mechanical system as detector of
stochastic force for short measurement times (for quick, high resolution
monitoring) as well as for the longer term observations that optimize the
sensitivity. We compare a simple, naive strategy based on the evaluation of the
variance of the displacement (that is a widely used technique) with an optimal
Wiener-Kolmogorov data analysis. We show that, thanks to the parametric
stabilization of the effective susceptibility, we can more efficiently
implement Wiener filtering, and we investigate how this strategy improves the
performance of our system. We finally demonstrate the possibility to resolve
stochastic force variations well below 1% of the thermal noise
An ultra-low dissipation micro-oscillator for quantum opto-mechanics
Generating non-classical states of light by opto-mechanical coupling depends
critically on the mechanical and optical properties of micro-oscillators and on
the minimization of thermal noise. We present an oscillating micro-mirror with
a mechanical quality factor Q = 2.6x10^6 at cryogenic temperature and a Finesse
of 65000, obtained thanks to an innovative approach to the design and the
control of mechanical dissipation. Already at 4 K with an input laser power of
2 mW, the radiation-pressure quantum fluctuations become the main noise source,
overcoming thermal noise. This feature makes our devices particularly suitable
for the production of pondero-motive squeezing.Comment: 21 pages including Supplementary Informatio
Correlated Component Analysis for diffuse component separation with error estimation on simulated Planck polarization data
We present a data analysis pipeline for CMB polarization experiments, running
from multi-frequency maps to the power spectra. We focus mainly on component
separation and, for the first time, we work out the covariance matrix
accounting for errors associated to the separation itself. This allows us to
propagate such errors and evaluate their contributions to the uncertainties on
the final products.The pipeline is optimized for intermediate and small scales,
but could be easily extended to lower multipoles. We exploit realistic
simulations of the sky, tailored for the Planck mission. The component
separation is achieved by exploiting the Correlated Component Analysis in the
harmonic domain, that we demonstrate to be superior to the real-space
application (Bonaldi et al. 2006). We present two techniques to estimate the
uncertainties on the spectral parameters of the separated components. The
component separation errors are then propagated by means of Monte Carlo
simulations to obtain the corresponding contributions to uncertainties on the
component maps and on the CMB power spectra. For the Planck polarization case
they are found to be subdominant compared to noise.Comment: 17 pages, accepted in MNRA
Harmonic damped oscillators with feedback. A Langevin study
We consider a system in direct contact with a thermal reservoir and which, if
left unperturbed, is well described by a memory-less equilibrium Langevin
equation of the second order in the time coordinate. In such conditions, the
strength of the noise fluctuations is set by the damping factor, in accordance
with the Fluctuation and Dissipation theorem. We study the system when it is
subject to a feedback mechanism, by modifying the Langevin equation
accordingly. Memory terms now arise in the time evolution, which we study in a
non-equilibrium steady state. Two types of feedback schemes are considered, one
focusing on time shifts and one on phase shifts, and for both cases we evaluate
the power spectrum of the system's fluctuations. Our analysis finds application
in feedback cooled oscillators, such as the Gravitational Wave detector AURIGA.Comment: 17 page
Dynamical two-mode squeezing of thermal fluctuations in a cavity opto-mechanical system
We report the experimental observation of two-mode squeezing in the
oscillation quadratures of a thermal micro-oscillator. This effect is obtained
by parametric modulation of the optical spring in a cavity opto-mechanical
system. In addition to stationary variance measurements, we describe the
dynamic behavior in the regime of pulsed parametric excitation, showing
enhanced squeezing effect surpassing the stationary 3dB limit. While the
present experiment is in the classical regime, our technique can be exploited
to produce entangled, macroscopic quantum opto-mechanical modes
Frequency noise cancellation in optomechanical systems for ponderomotive squeezing
Ponderomotive squeezing of the output light of an optical cavity has been
recently observed in the MHz range in two different cavity optomechanical
devices. Quadrature squeezing becomes particularly useful at lower spectral
frequencies, for example in gravitational wave interferometers, despite being
more sensitive to excess phase and frequency noise. Here we show a
phase/frequency noise cancellation mechanism due to destructive interference
which can facilitate the production of ponderomotive squeezing in the kHz range
and we demonstrate it experimentally in an optomechanical system formed by a
Fabry-P\'{e}rot cavity with a micro-mechanical mirror.Comment: 11 pages, 9 figures. Physical explanation expanded. Modified figure
Estimating the spectral indices of correlated astrophysical foregrounds by a second-order statistical approach
We present the first tests of a new method, the Correlated Component Analysis
(CCA) based on second-order statistics, to estimate the mixing matrix, a key
ingredient to separate astrophysical foregrounds superimposed to the Cosmic
Microwave Background (CMB). In the present application, the mixing matrix is
parameterized in terms of the spectral indices of Galactic synchrotron and
thermal dust emissions, while the free-free spectral index is prescribed by
basic physics, and is thus assumed to be known. We consider simulated
observations of the microwave sky with angular resolution and white stationary
noise at the nominal levels for the PLANCK satellite, and realistic foreground
emissions, with a position dependent synchrotron spectral index. We work with
two sets of PLANCK frequency channels: the low frequency set, from 30 to 143
GHz, complemented with the Haslam 408 MHz map, and the high frequency set, from
217 to 545 GHz. The concentration of intense free-free emission on the Galactic
plane introduces a steep dependence of the spectral index of the global
Galactic emission with Galactic latitude, close to the Galactic equator. This
feature makes difficult for the CCA to recover the synchrotron spectral index
in this region, given the limited angular resolution of PLANCK, especially at
low frequencies. A cut of a narrow strip around the Galactic equator (|b|<3
deg), however, allows us to overcome this problem. We show that, once this
strip is removed, the CCA allows an effective foreground subtraction, with
residual uncertainties inducing a minor contribution to errors on the recovered
CMB power spectrum.Comment: 9 pages, 5 figures and 1 table accepted by MNRA
Control of Recoil Losses in Nanomechanical SiN Membrane Resonators
In the context of a recoil damping analysis, we have designed and produced a
membrane resonator equipped with a specific on-chip structure working as a
"loss shield" for a circular membrane. In this device the vibrations of the
membrane, with a quality factor of , reach the limit set by the intrinsic
dissipation in silicon nitride, for all the modes and regardless of the modal
shape, also at low frequency. Guided by our theoretical model of the loss
shield, we describe the design rationale of the device, which can be used as
effective replacement of commercial membrane resonators in advanced
optomechanical setups, also at cryogenic temperatures
Calibrated quantum thermometry in cavity optomechanics
Cavity optomechanics has achieved the major breakthrough of the preparation
and observation of macroscopic mechanical oscillators in peculiarly quantum
states. The development of reliable indicators of the oscillator properties in
these conditions is important also for applications to quantum technologies. We
compare two procedures to infer the oscillator occupation number, minimizing
the necessity of system calibrations. The former starts from homodyne spectra,
the latter is based on the measurement of the motional sidebands asymmetry in
heterodyne spectra. Moreover, we describe and discuss a method to control the
cavity detuning, that is a crucial parameter for the accuracy of the latter,
intrinsically superior procedure
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