Knowledge of the spatio-temporal changes in the characteristics and distribution of subsurface fluids is key to properly addressing important societal issues, including: sustainable management of ...energy resources (e.g., hydrocarbons and geothermal energy), management of water resources, and assessment of hazard (e.g., volcanic eruptions). Gravimetry is highly attractive because it can detect changes in subsurface mass, thus providing a window into processes that involve deep fluids. However, high cost and operating features associated with current instrumentation seriously limits the practical field use of this geophysical method. The NEWTON-g project proposes a radical change of paradigm for gravimetry through the development of a field-compatible measuring system (the gravity imager), able to real-time monitor the evolution of the subsurface mass changes. This system includes an array of low-costs microelectromechanical systems-based relative gravimeters, anchored on an absolute quantum gravimeter. It will provide imaging of gravity changes, associated with variations in subsurface fluid properties, with unparalleled spatio-temporal resolution. During the final ∼2 years of NEWTON-g, the gravity imager will be field tested in the summit of Mt. Etna volcano (Italy), where frequent gravity fluctuations, easy access to the active structures and the presence of a multiparameter monitoring system (including traditional gravimeters) ensure an excellent natural laboratory for testing the new tools. Insights from the gravity imager will be used to i) improve our knowledge of the cause-effect relationships between volcanic processes and gravity changes observable at the surface and ii) develop strategies to best incorporate the gravity data into hazards assessments and mitigation plans. A successful implementation of NEWTON-g will open new doors for geophysical exploration.
A pivotal aspect in increasing the sensitivity of the Advanced LIGO detectors to allow the first gravitational wave detection, GW150914, was the installation of the monolithic fused silica ...suspensions. The 40 kg test mass suspended by four 400 μm fused silica fibres lowers the thermal noise as compared to initial LIGO. There is a desire for the use of thinner fibres to suspend smaller optics for other experiments of interest to the gravitational wave community that the current aLIGO fibre pulling machine is not capable of. We present here an overview of a new CO2 laser-based micron scale diameter fibre pulling machine developed at the University of Glasgow, based on the principals of our current aLIGO fibre pulling machine. We also discuss the upgraded fibre characterisation apparatus for dimensional and strength testing. It was found that fibres with a minimum diameter between 7.6 and 9.3 μm had an average breaking stress of 2.7 GPa and a Young's modulus value of 63.3 GPa, which is lower than the accepted bulk value of 72 GPa. Fibres with an average diameter between 13.2 and 17.8 μm had higher breaking stress and Young's modulus values ranging between 3.7-4.0 GPa and 71.8-75.9 GPa, respectively.
On April 1st, 2019, the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO), joined by the Advanced Virgo detector, began the third observing run, a year-long dedicated search for ...gravitational radiation. The LIGO detectors have achieved a higher duty cycle and greater sensitivity to gravitational waves than ever before, with LIGO Hanford achieving angle-averaged sensitivity to binary neutron star coalescences to a distance of 111 Mpc, and LIGO Livingston to 134 Mpc with duty factors of 74.6% and 77.0% respectively. The improvement in sensitivity and stability is a result of several upgrades to the detectors, including doubled intracavity power, the addition of an in-vacuum optical parametric oscillator for squeezed-light injection, replacement of core optics and end reaction masses, and installation of acoustic mode dampers. This paper explores the purposes behind these upgrades, and explains to the best of our knowledge the noise currently limiting the sensitivity of each detector.
Really cool mirrors
Cooling objects to low temperature can increase the sensitivity of sensors and the operational performance of most devices. Removing most of the thermal vibrations—or phonons—such ...that the object reaches its motional quantum ground state has been achieved but typically with tiny, nanoscale objects. Using the suspended mirrors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) that form a 10-kg optomechanical oscillator, Whittle
et al.
demonstrate the ability to cool such a large-scale object to nearly the motional ground state. An upgrade to LIGO with such a modification could increase its sensitivity and range to gravitational waves but also extend studies of quantum mechanics to large-scale objects.
Science
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A 10-kg mechanical oscillator, the mirror of LIGO, is cooled to near its motional quantum ground state.
The motion of a mechanical object, even a human-sized object, should be governed by the rules of quantum mechanics. Coaxing them into a quantum state is, however, difficult because the thermal environment masks any quantum signature of the object’s motion. The thermal environment also masks the effects of proposed modifications of quantum mechanics at large mass scales. We prepared the center-of-mass motion of a 10-kilogram mechanical oscillator in a state with an average phonon occupation of 10.8. The reduction in temperature, from room temperature to 77 nanokelvin, is commensurate with an 11 orders-of-magnitude suppression of quantum back-action by feedback and a 13 orders-of-magnitude increase in the mass of an object prepared close to its motional ground state. Our approach will enable the possibility of probing gravity on massive quantum systems.
The measurement of minuscule forces and displacements with ever greater precision is inhibited by the Heisenberg uncertainty principle, which imposes a limit to the precision with which the position ...of an object can be measured continuously, known as the standard quantum limit
. When light is used as the probe, the standard quantum limit arises from the balance between the uncertainties of the photon radiation pressure applied to the object and of the photon number in the photoelectric detection. The only way to surpass the standard quantum limit is by introducing correlations between the position/momentum uncertainty of the object and the photon number/phase uncertainty of the light that it reflects
. Here we confirm experimentally the theoretical prediction
that this type of quantum correlation is naturally produced in the Laser Interferometer Gravitational-wave Observatory (LIGO). We characterize and compare noise spectra taken without squeezing and with squeezed vacuum states injected at varying quadrature angles. After subtracting classical noise, our measurements show that the quantum mechanical uncertainties in the phases of the 200-kilowatt laser beams and in the positions of the 40-kilogram mirrors of the Advanced LIGO detectors yield a joint quantum uncertainty that is a factor of 1.4 (3 decibels) below the standard quantum limit. We anticipate that the use of quantum correlations will improve not only the observation of gravitational waves, but also more broadly future quantum noise-limited measurements.
The Advanced LIGO detectors have recently completed their second observation run successfully. The run lasted for approximately 10 months and led to multiple new discoveries. The sensitivity to ...gravitational waves was partially limited by laser noise. Here, we utilize auxiliary sensors that witness these correlated noise sources, and use them for noise subtraction in the time domain data. This noise and line removal is particularly significant for the LIGO Hanford Observatory, where the improvement in sensitivity is greater than 20%. Consequently, we were also able to improve the astrophysical estimation for the location, masses, spins, and orbital parameters of the gravitational wave progenitors.
Postpartum ovarian vein thrombosis, well described in the obstetrical literature with an incidence approaching 1 in 2,000 pregnancies, can present as a life-threatening complication. Although ...infrequent, thrombophlebitis of the ovarian vein may remain unrecognized and result in pulmonary embolism with dire outcome. Postpartum ovarian vein thrombosis can present initially as an acute ureteral obstruction, making it incumbent upon the urologist to recognize the entity with its associated radiological and clinical findings. A case report is presented to illustrate the disorder.