The first detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015 launched the era of gravitational-wave astronomy. The quest for gravitational-wave ...signals from objects that are fainter or farther away impels technological advances to realize ever more sensitive detectors. Since 2019, one advanced technique, the injection of squeezed states of light, is being used to improve the shot-noise limit to the sensitivity of the Advanced LIGO detectors, at frequencies above ∼50 Hz. Below this frequency, quantum backaction, in the form of radiation pressure induced motion of the mirrors, degrades the sensitivity. To simultaneously reduce shot noise at high frequencies and quantum radiation pressure noise at low frequencies requires a quantum noise filter cavity with low optical losses to rotate the squeezed quadrature as a function of frequency. We report on the observation of frequency-dependent squeezed quadrature rotation with rotation frequency of 30 Hz, using a 16-m-long filter cavity. A novel control scheme is developed for this frequency-dependent squeezed vacuum source, and the results presented here demonstrate that a low-loss filter cavity can achieve the squeezed quadrature rotation necessary for the next planned upgrade to Advanced LIGO, known as "A+."
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
, abh2634, this issue p.
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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.
In water-limited systems, pulses of rainfall can trigger a cascade of plant physiological responses. However, the timing and size of the physiological response can vary depending on plant and ...environmental characteristics, such as rooting depth, plant size, rainfall amount, or antecedent soil moisture. We investigated the influence of pulses of rainfall on the response of sap flow of two dominant evergreen tree species, Eucalyptus crebra (a broadleaf) and Callitris glaucophylla (a needle leaved tree), in a remnant open woodland in eastern Australia. Sap flow data were collected using heat-pulse sensors installed in six trees of each species over a 2 year period which encompassed the tail-end of a widespread drought. Our objectives were to estimate the magnitude that a rainfall pulse had to exceed to increase tree water use (i.e., define the threshold response), and to determine how tree and environmental factors influenced the increase in tree water use following a rainfall pulse. We used data filtering techniques to isolate rainfall pulses, and analysed the resulting data with multivariate statistical analysis. We found that rainfall pulses less than 20 mm did not significantly increase tree water use (P > 0.05). Using partial regression analysis to hold all other variables constant, we determined that the size of the rain event (P < 0.05, R ² = 0.59), antecedent soil moisture (P < 0.05, R ² = 0.29), and tree size (DBH, cm, P < 0.05, R ² = 0.15), all significantly affected the response to rainfall. Our results suggest that the conceptual Threshold-Delay model describing physiological responses to rainfall pulses could be modified to include these factors. We further conclude that modelling of stand water use over an annual cycle could be improved by incorporating the T-D behaviour of tree transpiration.
Melt inclusions (MI) are considered the best tool available for determining the pre-eruptive volatile contents of magmas. H2O and CO2 concentrations of the glass phase in MI are commonly used both as ...a barometer and to track magma degassing behavior during ascent due to the strong pressure dependence of H2O and CO2 solubilities in silicate melts. The often unstated and sometimes overlooked requirement for this method to be valid is that the glass phase in the MI must represent the composition of the melt that was trapped at depth in the volcanic plumbing system. However, melt inclusions commonly contain a vapor bubble that formed after trapping owing to differential shrinkage of the melt compared to the host crystal, and/or crystallization at the inclusion-host interface. Such bubbles may contain a substantial portion of volatiles, such as CO2, that were originally dissolved in the melt. In this study, we determined the contribution of CO2 in the vapor bubble to the overall CO2 content of MI based on quantitative Raman analysis of the vapor bubbles in MI from the 1959 Kilauea Iki (Hawaii), 1960 Kapoho (Hawaii), 1974 Fuego volcano (Guatemala), and 1977 Seguam Island (Alaska) eruptions. We found that the bubbles typically contain 40 to 90% of the total CO2 in the MI. Reconstructing the original CO2 content by adding the CO2 in the bubble back into the melt results in an increase in CO2 concentration by as much as an order of magnitude (thousands of parts per million). Reconstructed CO2 concentrations correspond to trapping pressures that are significantly greater than one would predict based on analysis of the volatiles in the glass alone. Trapping depths can be as much as 10 km deeper than estimates that ignore the CO2 in the bubble. In addition to CO2 in the vapor bubbles, many MI showed the presence of a carbonate mineral phase. Failure to recognize the carbonate during petrographic examination or analysis of the glass and to include its contained CO2 when reconstructing the CO2 content of the originally trapped melt will introduce additional errors into the calculated volatile budget. Our results emphasize that accurate determination of the pre-eruptive volatile content of melts based on analysis of melt inclusions must consider the volatiles contained in the bubble (and carbonates, if present). This can be accomplished either by analysis of the bubble and the glass followed by mass-balance reconstruction of the original volatile content of the melt, or by re-homogenization of the MI prior to conducting microanalysis of the quenched, glassy MI.
Melt inclusions (MI) represent the best source of information concerning the pre-eruptive volatile contents of magmas. If the trapped melt is enriched in volatile species, following trapping the MI ...may generate a vapor bubble containing volatiles that have exsolved from the melt. Thermodynamic modeling of vapor-saturated albitic composition (NaAlSi3O8) MI shows that the CO2 content of the melt phase in the MI is sensitive to small amounts of post-entrapment crystallization (PEC), whereas the H2O content of the melt is less sensitive to PEC. During PEC, CO2 is transferred from the melt to the vapor phase and the vapor bubble may contain a significant amount, if not most, of the CO2 in the MI. The contrasting behaviors of H2O and CO2 during PEC lead to H2O-CO2 trends that are similar to those predicted for open-system degassing during magma ascent and decompression. Thus, similar H2O-CO2 trends may be produced if (1) vapor-saturated MI are trapped at various depths along a magmatic ascent path, or (2) MI having the same volatile content are all trapped at the same depth, but undergo different amounts of PEC following trapping. It is not possible to distinguish between these two contrasting interpretations based on MI volatile data alone. However, by examining the volatile trends within the context of other geochemical monitors of crystallization or magma evolution progress, it may be possible to determine whether the volatile trends were generated along a degassing path or if they reflect various amounts of PEC in an originally homogeneous melt inclusion assemblage. The volatile trends resulting from PEC of MI described in this study are directly applicable to silica-rich (granitic) MI trapped in non-ferromagnesian host phases, and are only qualitatively applicable to more mafic melt compositions and/or host phases owing to modifications resulting from Fe exchange with the host and to post-entrapment re-equilibration processes.
Land-use change alters catchment hydrology by influencing the quality and quantity of partitioned rainfall. We compared rainfall partitioning (throughfall, stemflow and interception) and nutrient ...concentrations in rainfall, throughfall and stemflow in three land-use types primary forest (PF), secondary forest (SF) and agriculture (A) in Panama. Measurements of throughfall were highly variable which may have masked seasonal and land use differences but it was clear that throughfall at agricultural sites made up a larger proportion of gross precipitation than at forest sites. Of incident precipitation, 94% became throughfall in agriculture sites while 83 and 81% of gross precipitation became throughfall in PF and SF, respectively. The size of the precipitation event was the main driver of variation in throughfall and stemflow. Consistent patterns in nutrient cycling were also difficult to identify. Vegetation has a vital role in delivering nutrients as throughfall deposition of K was often larger than precipitation deposition. A canopy budget model indicated that canopy exchange was often more dominant than dry deposition. Throughfall was generally enriched with nutrients, especially K and Mg, with enrichment factors of up to 17 and 5 for K and Mg, respectively, in PF. In contrast, Ca was sometimes taken up by the canopy. Values of nutrient deposition were high (with up to 15, 3, 30 and 15 kg ha -1 month -1 in stand deposition of Ca, Mg, K and Na, respectively in PF), possibly due to the slash- and-burn agricultural practices in the area or marine inputs. Throughfall and stemflow are vital sources of nutrients in these ecosystems.
Various thermodynamic properties of H2O that are defined as pressure or temperature derivatives of some other variable, such as isothermal compressibility (β, pressure derivative of density), ...isobaric thermal expansion (α, temperature derivative of density), and specific isobaric heat capacity (cf, temperature derivative of enthalpy), all show large magnitudes near the critical point, reflecting large variations in fluid density and specific enthalpy with small changes in temperature and pressure. As a result, mass (related to fluid density) and energy (related to fluid enthalpy) transport in this PT region are sensitive to changing PT conditions. Addition of NaCl to H2O causes the region of anomalous behavior, here defined as the critical region, to migrate to higher temperatures and pressures. The critical region is defined as that region of PT space in which the dimensionless reduced susceptibility χ~ ≥ 0.5. When NaCl is added to H2O, the critical region migrates to higher temperature and pressure. However, the absolute magnitudes of thermodynamic properties that are defined as temperature and/or pressure derivatives (α, β, and cf) all decrease with increasing salinity. Thus, the mass and energy transporting capacities of hydrothermal fluids in the critical region become less sensitive to changing PT conditions as the salinity increases. For example, quartz solubility can be described as a function of fluid density, and because density becomes less sensitive to changing PT conditions as salinity increases, quartz solubility also becomes less sensitive to changing PT conditions as fluid salinity increases. Similarly, fluxibility describes the ability of a fluid to transport heat by buoyancy‐driven convection, and fluxibility decreases with increasing salinity. Results of this study show that the mass and energy transport capacity of fluids in the Earth's crust are maximized in the critical region and that the sensitivity to changing PT conditions decreases with increasing salinity.
Pure H2O exhibits anomalous behavior in the vicinity of the critical point, reflected by large variations in density and specific enthalpy with small changes in temperature and pressure. Mass and energy transport properties that are temperature or pressure derivatives of density and specific enthalpy thus show large variability near the critical point. Addition of NaCl to H2O causes the critical region in which fluid properties exhibit anomalous behavior to migrate to higher temperatures and pressures.
The two-stage vibration isolation and positioning platform provides passive and active isolation in all directions and translation. It uses a unique combination of position sensors, geophones and ...broadband seismometers to provide unprecedented levels of isolation.
•The paper presents the two-stage vibration isolation and positioning platform used in Advanced LIGO gravitational waves detectors.•The system can support a 1000kg of sensitive equipment and operate in ultra-high vacuum.•Each of the two stages provide passive and active isolation in all directions of translation and rotation (12 axis).•The active control strategy uses a unique combination of relative sensors, geophones and broadband seismometers.•The system reduces the motion to the level of 10−11 m/Hz at 1Hz and 10−12 m/Hz at 10Hz.
New generations of gravity wave detectors require unprecedented levels of vibration isolation. This paper presents the final design of the vibration isolation and positioning platform used in Advanced LIGO to support the interferometer's core optics. This five-ton two-and-half-m wide system operating in ultra-high vacuum. It features two stages of isolation mounted in series. The stages are imbricated to reduce the overall height. Each stage provides isolation in all directions of translation and rotation. The system is instrumented with a unique combination of low noise relative and inertial sensors. The active control provides isolation from 0.1Hz to 30Hz. It brings the platform motion down to 10−11 m/Hz at 1Hz. Active and passive isolation combine to bring the platform motion below 10−12 m/Hz at 10Hz. The passive isolation lowers the motion below 10−13 m/Hz at 100Hz. The paper describes how the platform has been engineered not only to meet the isolation requirements, but also to permit the construction, testing, and commissioning process of the fifteen units needed for Advanced LIGO observatories.
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