148 research outputs found
LIGO’s quantum response to squeezed states
Gravitational Wave interferometers achieve their profound sensitivity by combining a Michelson interferometer with optical cavities, suspended masses, and now, squeezed quantum states of light. These states modify the measurement process of the LIGO, VIRGO and GEO600 interferometers to reduce the quantum noise that masks astrophysical signals; thus, improvements to squeezing are essential to further expand our gravitational view of the universe. Further reducing quantum noise will require both lowering decoherence from losses as well more sophisticated manipulations to counter the quantum back-action from radiation pressure. Both tasks require fully understanding the physical interactions between squeezed light and the many components of km-scale interferometers. To this end, data from both LIGO observatories in observing run three are expressed using frequency-dependent metrics to analyze each detector's quantum response to squeezed states. The response metrics are derived and used to concisely describe physical mechanisms behind squeezing's simultaneous interaction with transverse-mode selective optical cavities and the quantum radiation pressure noise of suspended mirrors. These metrics and related analysis are broadly applicable for cavity-enhanced optomechanics experiments that incorporate external squeezing, and -- for the first time -- give physical descriptions of every feature so far observed in the quantum noise of the LIGO detectors
Point absorbers in Advanced LIGO
Small, highly absorbing points are randomly present on the surfaces of the main interferometer optics in Advanced LIGO. The resulting nanometer scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduce the sensitivity of the interferometer directly though a reduction in the power-recycling gain and indirect interactions with the feedback control system. We review the expected surface deformation from point absorbers and provide a pedagogical description of the impact on power buildup in second generation gravitational wave detectors (dual-recycled Fabry–Perot Michelson interferometers). This analysis predicts that the power-dependent reduction in interferometer performance will significantly degrade maximum stored power by up to 50% and, hence, limit GW sensitivity, but it suggests system wide corrections that can be implemented in current and future GW detectors. This is particularly pressing given that future GW detectors call for an order of magnitude more stored power than currently used in Advanced LIGO in Observing Run 3. We briefly review strategies to mitigate the effects of point absorbers in current and future GW wave detectors to maximize the success of these enterprises
Approaching the motional ground state of a 10 kg object
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: the thermal environment masks any quantum signature of
the object's motion. Indeed, the thermal environment also masks effects of
proposed modifications of quantum mechanics at large mass scales. We prepare
the center-of-mass motion of a 10 kg mechanical oscillator in a state with an
average phonon occupation of 10.8. The reduction in temperature, from room
temperature to 77 nK, 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.
This begets the possibility of probing gravity on massive quantum systems.Comment: published version containing minor change
Quantum correlations between the light and kilogram-mass mirrors of LIGO
Measurement of minuscule forces and displacements with ever greater precision
encounters a limit imposed by a pillar of quantum mechanics: the Heisenberg
uncertainty principle. A limit to the precision with which the position of an
object can be measured continuously is known as the standard quantum limit
(SQL). When light is used as the probe, the SQL arises from the balance between
the uncertainties of photon radiation pressure imposed on the object and of the
photon number in the photoelectric detection. The only possibility surpassing
the SQL is via correlations within the position/momentum uncertainty of the
object and the photon number/phase uncertainty of the light it reflects. Here,
we experimentally prove the theoretical prediction that this type of quantum
correlation is naturally produced in the Laser Interferometer
Gravitational-wave Observatory (LIGO). Our measurements show that the quantum
mechanical uncertainties in the phases of the 200 kW laser beams and in the
positions of the 40 kg mirrors of the Advanced LIGO detectors yield a joint
quantum uncertainty a factor of 1.4 (3dB) below the SQL. We anticipate that
quantum correlations will not only improve gravitational wave (GW)
observatories but all types of measurements in future
Sensitivity and Performance of the Advanced LIGO Detectors in the Third Observing Run
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.Comment: 27 pages, 11 figures. v2 edits: minor wording changes, author
additions, and grayscale-friendly figure
Environmental Noise in Advanced LIGO Detectors
The sensitivity of the Advanced LIGO detectors to gravitational waves can be
affected by environmental disturbances external to the detectors themselves.
Since the transition from the former initial LIGO phase, many improvements have
been made to the equipment and techniques used to investigate these
environmental effects. These methods have aided in tracking down and mitigating
noise sources throughout the first three observing runs of the advanced
detector era, keeping the ambient contribution of environmental noise below the
background noise levels of the detectors. In this paper we describe the methods
used and how they have led to the mitigation of noise sources, the role that
environmental monitoring has played in the validation of gravitational wave
events, and plans for future observing runs
Quantum-enhanced advanced LIGO detectors in the era of gravitational-wave astronomy
The Laser Interferometer Gravitational Wave Observatory (LIGO) has been directly detecting gravitational waves from compact binary mergers since 2015. We report on the first use of squeezed vacuum states in the direct measurement of gravitational waves with the Advanced LIGO H1 and L1 detectors. This achievement is the culmination of decades of research to implement squeezed states in gravitational-wave detectors. During the ongoing O3 observation run, squeezed states are improving the sensitivity of the LIGO interferometers to signals above 50 Hz by up to 3 dB, thereby increasing the expected detection rate by 40% (H1) and 50% (L1)
All-sky search for long-duration gravitational-wave bursts in the third Advanced LIGO and Advanced Virgo run
After the detection of gravitational waves from compact binary coalescences, the search for transient gravitational-wave signals with less well-defined waveforms for which matched filtering is not well suited is one of the frontiers for gravitational-wave astronomy. Broadly classified into “short” ≲1 s and “long” ≳1 s duration signals, these signals are expected from a variety of astrophysical processes, including non-axisymmetric deformations in magnetars or eccentric binary black hole coalescences. In this work, we present a search for long-duration gravitational-wave transients from Advanced LIGO and Advanced Virgo’s third observing run from April 2019 to March 2020. For this search, we use minimal assumptions for the sky location, event time, waveform morphology, and duration of the source. The search covers the range of 2–500 s in duration and a frequency band of 24–2048 Hz. We find no significant triggers within this parameter space; we report sensitivity limits on the signal strength of gravitational waves characterized by the root-sum-square amplitude hrss as a function of waveform morphology. These hrss limits improve upon the results from the second observing run by an average factor of 1.8
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