Around the globe several observatories are seeking the first direct detection of gravitational waves (GWs). These waves are predicted by Einstein's general theory of relativity and are generated, for ...example, by black-hole binary systems. Present GW detectors are Michelson-type kilometre-scale laser interferometers measuring the distance changes between mirrors suspended in vacuum. The sensitivity of these detectors at frequencies above several hundred hertz is limited by the vacuum (zero-point) fluctuations of the electromagnetic field. A quantum technology--the injection of squeezed light--offers a solution to this problem. Here we demonstrate the squeezed-light enhancement of GEO 600, which will be the GW observatory operated by the LIGO Scientific Collaboration in its search for GWs for the next 3-4 years. GEO 600 now operates with its best ever sensitivity, which proves the usefulness of quantum entanglement and the qualification of squeezed light as a key technology for future GW astronomy.
Abstract
We report on the development and extensive characterization of co-sputtered tantala–zirconia (Ta
2
O
5
-ZrO
2
) thin films, with the goal to decrease coating Brownian noise in present and ...future gravitational-wave detectors. We tested a variety of sputtering processes of different energies and deposition rates, and we considered the effect of different values of cation ratio
η
= Zr/(Zr + Ta) and of post-deposition heat treatment temperature
T
a
on the optical and mechanical properties of the films. Co-sputtered zirconia proved to be an efficient way to frustrate crystallization in tantala thin films, allowing for a substantial increase of the maximum annealing temperature and hence for a decrease of coating mechanical loss
φ
c
. The lowest average coating loss was observed for an ion-beam sputtered sample with
η
= 0.485 ± 0.004 annealed at 800 °C, yielding
φ
¯
c
=
1.8
×
1
0
−
4
rad. All coating samples showed cracks after annealing. Although in principle our measurements are sensitive to such defects, we found no evidence that our results were affected. The issue could be solved, at least for ion-beam sputtered coatings, by decreasing heating and cooling rates down to 7 °C h
−1
. While we observed as little optical absorption as in the coatings of current gravitational-wave interferometers (0.5 parts per million), further development will be needed to decrease light scattering and avoid the formation of defects upon annealing.
Advanced LIGO Abbott, R; Addesso, P; Aggarwal, N ...
Classical and quantum gravity,
04/2015, Letnik:
32, Številka:
7
Journal Article, Web Resource
Recenzirano
Odprti dostop
The Advanced LIGO gravitational wave detectors are second-generation instruments designed and built for the two LIGO observatories in Hanford, WA and Livingston, LA, USA. The two instruments are ...identical in design, and are specialized versions of a Michelson interferometer with 4 km long arms. As in Initial LIGO, Fabry-Perot cavities are used in the arms to increase the interaction time with a gravitational wave, and power recycling is used to increase the effective laser power. Signal recycling has been added in Advanced LIGO to improve the frequency response. In the most sensitive frequency region around 100 Hz, the design strain sensitivity is a factor of 10 better than Initial LIGO. In addition, the low frequency end of the sensitivity band is moved from 40 Hz down to 10 Hz. All interferometer components have been replaced with improved technologies to achieve this sensitivity gain. Much better seismic isolation and test mass suspensions are responsible for the gains at lower frequencies. Higher laser power, larger test masses and improved mirror coatings lead to the improved sensitivity at mid and high frequencies. Data collecting runs with these new instruments are planned to begin in mid-2015.
Thermo-optic noise is likely to be the dominant noise source in next generation ultralow noise optical cavities. We developed three measurement and analysis methods, allowing us to estimate the level ...of coating thermo-optic noise in optical cavities, including interferometric gravitational wave detectors. We measured the shift in the broadband transmission spectra as a function of temperature for single-layer, high index coatings in order to find the thermo-optic coefficient, βH, of a coating while assuming the thermal expansion coefficient, αH. Our value for βH could then be used to calculate the thermo-optic noise in any high-finesse optical cavity using coatings with the same high index layer material. We also measured the spectra as a function of temperature of a multilayer, high-reflectivity coating where the material composition of the layers was similar to the coatings installed in Advanced LIGO. This method has the advantage of allowing us to calculate thermo-optic noise directly; αH and βH do not need to be known separately, although we do need to know the value of the overall coating thermal expansion coefficient. Finally, we used lasers of different wavelengths to measure transmission changes on the band edges of a multilayer high-reflectivity coating. This gave measurements with high statistical precision but potentially lower systematic accuracy. To address systematic accuracy concerns, we used a constrained Monte Carlo application of the theory of multilayer coating transmission.
We have compiled measurements of the mechanical loss in fused silica from samples spanning a wide range of geometries and resonant frequency in order to model the known variation of the loss with ...frequency and surface-to-volume ratio. This improved understanding of the mechanical loss has contributed significantly to the design of advanced interferometric gravitational wave detectors, which require ultra-low loss materials for their test mass mirrors.
Abstract
α
-RuCl
3
is a major candidate for the realization of the Kitaev quantum spin liquid, but its zigzag antiferromagnetic order at low temperatures indicates deviations from the Kitaev model. ...We have quantified the spin Hamiltonian of
α
-RuCl
3
by a resonant inelastic x-ray scattering study at the Ru
L
3
absorption edge. In the paramagnetic state, the quasi-elastic intensity of magnetic excitations has a broad maximum around the zone center without any local maxima at the zigzag magnetic Bragg wavevectors. This finding implies that the zigzag order is fragile and readily destabilized by competing ferromagnetic correlations. The classical ground state of the experimentally determined Hamiltonian is actually ferromagnetic. The zigzag state is stabilized by quantum fluctuations, leaving ferromagnetism – along with the Kitaev spin liquid – as energetically proximate metastable states. The three closely competing states and their collective excitations hold the key to the theoretical understanding of the unusual properties of
α
-RuCl
3
in magnetic fields.
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