G. A. Prodi

Localization of gravitational wave sources with networks of advanced detectors

Coincident observations with gravitational wave (GW) detectors and other astronomical instruments are among the main objectives of the experiments with the network of LIGO, Virgo, and GEO detectors. They will become a necessary part of the future GW astronomy as the next generation of advanced detectors comes online. The success of such joint observations directly depends on the source localization capabilities of the GW detectors. In this paper we present studies of the sky localization of transient GW sources with the future advanced detector networks and describe their fundamental properties. By reconstructing sky coordinates of ad hoc signals injected into simulated detector noise, we study the accuracy of the source localization and its dependence on the strength of injected signals, waveforms, and network configurations.

Method for detection and reconstruction of gravitational wave transients with networks of advanced detectors

We present a method for detection and reconstruction of the gravitational-wave (GW) transients with the networks of advanced detectors. Originally designed to search for transients with the initial GW detectors, it uses signicantly improved algorithms, which enhances both the low-latency searches with rapid localization of GW events for the electro-magnetic followup and high condence detection of a broad range of the transient GW sources. In the paper we present the analytic framework of the method. Following a short description of the core analysis algorithms, we introduce a novel approach to the reconstruction of the GW polarization from a pattern of detector responses to a GW signal. This polarization pattern is a unique signature of an arbitrary GW signal that can be measured independent from the other source parameters. The polarization measurements enable rapid reconstruction of the GW waveforms, sky localization and helps identication of the source origin.

Feedback Cooling of the Normal Modes of a Massive Electromechanical System to Submillikelvin Temperature

We apply a feedback cooling technique to simultaneously cool the three electromechanical normal modes of the ton-scale resonant-bar gravitational wave detector AURIGA. The measuring system is based on a dc superconducting quantum interference device (SQUID) amplifier, and the feedback cooling is applied electronically to the input circuit of the SQUID. Starting from a bath temperature of 4.2 K, we achieve a minimum temperature of 0.17 mK for the coolest normal mode. The same technique, implemented in a dedicated experiment at subkelvin bath temperature and with a quantum limited SQUID, could allow to approach the quantum ground state of a kilogram-scale mechanical resonator.

3-Mode Detection for Widening the Bandwidth of Resonant Gravitational Wave Detectors

Along with peak sensitivity, an important parameter of a resonant gravitational wave detector is its bandwidth. In addition to the obvious advantage of making the detector more sensitive to short bursts, a wider bandwidth would allow, for instance, details of the signal emitted during a supernova gravitational collapse or the merger of compact binaries to be resolved [1]. Moreover, a wider bandwidth reduces the uncertainty in the burst arrival time [2] and consequently, with a detector network, permits a more precise source location and a higher efficiency of spurious events rejection [3]. The introduction of a mechanically resonant transducer, a standard practice in actual resonant detectors, has greatly improved the coupling between the bar and the amplifier, but the bandwidth is intrinsically limited [4], and in practice, according to the full width at half maximum (FWHM) definition applied to the two minima of the Shh strain noise spectra, values of a few Hz have been achieved [5]. The use of multimode resonant transducers should permit further improvements of the detector bandwidth [6]. This approach has been studied [7] in depth and a few 2-mode transducer prototypes have been realized [8] or are under development [9] to obtain 3mode operation of the resonant mass detectors. This Letter describes how a wider detection bandwidth can be obtained with an alternative 2-mode transduction system in which the resonant amplification is realized by means of a resonant mechanical mode plus a resonant electrical matching network. It also describes the key tests performed on the components of the transduction system in order to verify the achievement of the requirements set by analysis of the detector model. Figure 1 shows the electromechanical scheme of a cryogenic detector with a resonant capacitive transducer read by a SQUID amplifier. The matching transformer couples the output impedance of the transducer (a capacitance of a few nF) to the input impedance of the SQUID (a small

Probing deformed commutators with macroscopic harmonic oscillators.

A minimal observable length is a common feature of theories that aim to merge quantum physics and gravity. Quantum mechanically, this concept is associated with a nonzero minimal uncertainty in position measurements, which is encoded in deformed commutation relations. In spite of increasing theoretical interest, the subject suffers from the complete lack of dedicated experiments and bounds to the deformation parameters have just been extrapolated from indirect measurements. As recently proposed, low-energy mechanical oscillators could allow to reveal the effect of a modified commutator. Here we analyze the free evolution of high-quality factor micro- and nano-oscillators, spanning a wide range of masses around the Planck mass mP (≈22 μg). The direct check against a model of deformed dynamics substantially lowers the previous limits on the parameters quantifying the commutator deformation.

Squeezing a Thermal Mechanical Oscillator by Stabilized Parametric Effect on the Optical Spring

We report the confinement of an optomechanical micro-oscillator in a squeezed thermal state, obtained by parametric modulation of the optical spring. We propose and implement an experimental scheme based on parametric feedback control of the oscillator, which stabilizes the amplified quadrature while leaving the orthogonal one unaffected. This technique allows us to surpass the -3  dB limit in the noise reduction, associated with parametric resonance, with a best experimental result of -7.4  dB. While the present experiment is in the classical regime, in a moderately cooled system our technique may allow squeezing of a macroscopic mechanical oscillator below the zero-point motion.

Status report and near future prospects for the gravitational wave detector AURIGA

We describe the experimental efforts to set up the second AURIGA run. Thanks to the upgraded capacitive readout, fully characterized and optimized in a dedicated facility, we predict an improvement in the detector sensitivity and bandwidth by at least one order of magnitude. In the second run, AURIGA will also benefit from newly designed cryogenic mechanical suspensions and the upgraded data acquisition and data analysis.

Dragging of inertial frames by the rotating Earth: Proposal and feasibility for a ground-based detection

We are proposing a ground-based experiment to detect the Lense-Thirring drag due to the rotating earth by an off-line comparison between an astrometric measurement of the Earth rotation and an inertial measurement of the angular velocity of the laboratory. It is shown that the former, by means of routine observations of Very Long Baseline Interferometry, has already reached the accuracy needed to perform a 3 % experiment on a time span of ∼1 yr. We propose to perform the latter by a dynamical detector of local rotation of novel conception, the Gyromagnetic Electron Gyroscope. Its principle of operation is briefly discussed together with its response to rotationlike gravitational fields.

Selective readout and back-action reduction for wideband acoustic gravitational wave detectors

We present the concept of the ‘‘selective readout’’ for the recently proposed dual detector @M. Cerdonio et al., Phys. Rev. Lett. 87, 031101 ~2001!# of gravitational waves which is a sensitive and broadband resonantmass detector. The advantage of the proposed detection scheme is that it is made sensitive only to the acoustic modes of the masses forming the detector that have quadrupolar symmetry, and thus carry the signal, while it rejects efficiently the noise contribution from the other modes, either of thermal or back-action origin. The total effect is that the sensitivity of a dual detector equipped with the selective readout is flat within a wide frequency range and can be as good as ;8310 224 /AHz between 1.3 and 4 kHz for a silicon carbide detector, 3 m in diameter.

Ultralow-dissipation micro-oscillator for quantum optomechanics

Generating nonclassical states of light by optomechanical coupling depends critically on the mechanical and optical properties of micro-oscillators and on the minimization of thermal noise. We present an oscillating micromirror with a mechanical quality factor