We present the MIGA experiment, an underground long baseline atom interferometer to study gravity at large scale. The hybrid atom-laser antenna will use several atom interferometers simultaneously interrogated by the resonant mode of an optical cavity. The instrument will be a demonstrator for gravitational wave detection in a frequency band (100 mHz–1 Hz) not explored by classical ground and space-based observatories, and interesting for potential astrophysical sources. In the initial instrument configuration, standard atom interferometry techniques will be adopted, which will bring to a peak strain sensitivity of at 2 Hz. This demonstrator will enable to study the techniques to push further the sensitivity for the future development of gravitational wave detectors based on large scale atom interferometers. The experiment will be realized at the underground facility of the Laboratoire Souterrain à Bas Bruit (LSBB) in Rustrel–France, an exceptional site located away from major anthropogenic disturbances and showing very low background noise. In the following, we present the measurement principle of an in-cavity atom interferometer, derive the method for Gravitational Wave signal extraction from the antenna and determine the expected strain sensitivity. We then detail the functioning of the different systems of the antenna and describe the properties of the installation site.
At periods greater than 1000 seconds, Earth's seismic free oscillations have anomalously large amplitude when referenced to the Harvard Centroid Moment Tensor fault mechanism, which is estimated from 300- to 500-second surface waves. By using more realistic rupture models on a steeper fault derived from seismic body and surface waves, we approximated free oscillation amplitudes with a seismic moment (6.5 x 10(22) Newton.meters) that corresponds to a moment magnitude of 9.15. With a rupture duration of 600 seconds, the fault-rupture models represent seismic observations adequately but underpredict geodetic displacements that argue for slow fault motion beneath the Nicobar and Andaman islands.
Gravitational waves (GWs) were observed for the first time in 2015, one century after Einstein predicted their existence. There is now growing interest to extend the detection bandwidth to low frequency. The scientific potential of multi-frequency GW astronomy is enormous as it would enable to obtain a more complete picture of cosmic events and mechanisms. This is a unique and entirely new opportunity for the future of astronomy, the success of which depends upon the decisions being made on existing and new infrastructures. The prospect of combining observations from the future space-based instrument LISA together with third generation ground based detectors will open the way toward multi-band GW astronomy, but will leave the infrasound (0.1–10 Hz) band uncovered. GW detectors based on matter wave interferometry promise to fill such a sensitivity gap. We propose the European Laboratory for Gravitation and Atom-interferometric Research (ELGAR), an underground infrastructure based on the latest progress in atomic physics, to study space–time and gravitation with the primary goal of detecting GWs in the infrasound band. ELGAR will directly inherit from large research facilities now being built in Europe for the study of large scale atom interferometry and will drive new pan-European synergies from top research centers developing quantum sensors. ELGAR will measure GW radiation in the infrasound band with a peak strain sensitivity of
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0
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at 1.7 Hz. The antenna will have an impact on diverse fundamental and applied research fields beyond GW astronomy, including gravitation, general relativity, and geology.
International audienceSince the beginning of the Global Geodynamics Project (GGP) in 1997, the number of superconducting gravimeters (SGs) has increased to reach 30 operating sites today. Data from this network allow a comparison of the noise levels of the different contributing stations. The knowledge of the noise levels at each site is important in any combination of data to determine global Earth parameters, for example, the stacking of the data in the search for elusive signals, like the gravity variations associated with the translational mode of the inner core. We use a standardized procedure based on the computation of the residual power spectral densities (PSDs) over a quiet time period in order to evaluate the combined instrument plus site noise in the long-period seismic band (0.3 mHz-1 mHz). The experience at Strasbourg (France) has shown some improvements from the TT70-T005 full-size instrument to the C026 compact model in terms of noise reduction, while the most recent Observatory SG types, OSG044 at Bad Homburg (Germany) and OSG052 at Sutherland (South Africa), do not show any further improvement with respect to the compact models, respectively CD30 and CD037, operating at the same stations. At Black Forest Observatory (BFO) in Germany, the experience of the dual-sphere OSG with a lower sphere heavier than usual has shown that the instrumental and site conditions make this station the least noisy one at frequencies larger than 0.1 mHz. The noise analysis using the longest time-series available has shown that the noise level at these sites is mostly stable (within 1σ) over the years. The comparison with some seismological noise models shows that the best SG sites are less noisy than longperiod seismometers below 1 mHz. However, the noise level of the best SGs is still at the limit of detection of the subseismic translational mode of the inner core
The recent Peru earthquake with a moment magnitude Mw = 8.4 on June 23, 2001 presents a good opportunity for the observation of the seismic gravest normal modes. For the longest periods, below 1 mHz Superconducting Gravimeters (SGs) have been shown to be less noisy than long‐period seismometers. A stack based on the spatial and temporal properties of the modes of degree one in a spherical harmonic development applied to 164 h of common records at the Cantley, Canberra, Strasbourg, Sutherland and Vienna SG stations has led to the first clear observation of the 2S1 long‐period seismic modes with a central frequency close to 0.4 mHz. Moreover the spectrum of the SG record at the Strasbourg station confirms the benefit SGs can provide to normal mode seismology with the clear observation of the splitting of the fundamental mode 0S2 into 5 fairly well resolved singlets with only one record.
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