Antenna pattern of DUAL detectors of gravitational waves and its exploitation in a network of advanced interferometers

We investigate the directional sensitivity to plane gravitational waves (GWs) of DUAL detectors of cylindrical shape. Calculations make use of the finite element method to simulate the responses to the GW Riemann tensor of a single-mass DUAL (SMD) and of a tapered cylinder (TC) in their wide sensitivity bandwidth. We show that one SMD or a pair of TCs is able to cover both GW polarization amplitudes from almost all incoming directions. We discuss the achievable enhancement in tackling the inverse problem for high frequency [~(2–5) kHz] GWs by adding a TC detector to the future advanced LIGO–VIRGO network

False discovery rate: setting the probability of false claim of detection

When testing multiple hypothesis in a survey --e.g. many different source locations, template waveforms, and so on-- the final result consists in a set of confidence intervals, each one at a desired confidence level. But the probability that at least one of these intervals does not cover the true value increases with the number of trials. With a sufficiently large array of confidence intervals, one can be sure that at least one is missing the true value. In particular, the probability of false claim of detection becomes not negligible. In order to compensate for this, one should increase the confidence level, at the price of a reduced detection power. False discovery rate control is a relatively new statistical procedure that bounds the number of mistakes made when performing multiple hypothesis tests. We shall review this method, discussing exercise applications to the field of gravitational wave surveys.Comment: 7 pages, 3 table, 3 figures. Prepared for the Proceedings of GWDAW 9 (http://lappc-in39.in2p3.fr/GWDAW9) A new section was added with a numerical example, along with two tables and a figure related to the new section. Many smaller revisions to improve readibilit

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

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

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

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

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 $10^7$, 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

DNA quantification to assess Zymoseptoria tritici on a susceptible cultivar of durum wheat to establish the best timing for fungicide application in an italian environment

Zymoseptoria tritici, a globally distributed pathogen, is responsible of Septoria tritici blotch (STB), one of the most damaging wheat diseases. In Italy the incidence of STB has increased during the past few years. The presence of Z. tritici on flag leaves of susceptible durum wheat plants, cultivar San Carlo, after a single artificial inoculation with two inoculum concentrations at different vegetative stages has been evaluated in the plain of Bologna (North of Italy), in a two year field study (2012–2013). The pathogen presence was also assessed in natural infection conditions after a fungicide application in the second year (2013). The results obtained, by visual examination (Incidence, Disease Severity) and DNA quantification by Real time PCR, demonstrated that BBCH 39 (flag leaf stage) is the most susceptible vegetative stage, independently of inoculum concentration and climatic conditions. A good correlation between Disease Severity and DNA quantity was observed in either sampling methods, entire flag leaves and flag leaf discs. Thereafter the most suitable period to obtain the best crop protection with only one fungicide treatment is the flag leaf stage

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