9,368 research outputs found
Towards the Design of Gravitational-Wave Detectors for Probing Neutron-Star Physics
The gravitational waveform of merging binary neutron stars encodes
information about extreme states of matter. Probing these gravitational
emissions requires the gravitational-wave detectors to have high sensitivity
above 1 kHz. Fortunately for current advanced detectors, there is a sizeable
gap between the quantum-limited sensitivity and the classical noise at high
frequencies. Here we propose a detector design that closes such a gap by
reducing the high-frequency quantum noise with an active optomechanical filter,
frequency-dependent squeezing, and high optical power. The resulting noise
level from 1 kHz to 4 kHz approaches the current facility limit and is a factor
of 20 to 30 below the design of existing advanced detectors. This will allow
for precision measurements of (i) the post-merger signal of the binary neutron
star, (ii) late-time inspiral, merger, and ringdown of low-mass black
hole-neutron star systems, and possible detection of (iii) high-frequency modes
during supernovae explosions. This design tries to maximize the science return
of current facilities by achieving a sensitive frequency band that is
complementary to the longer-baseline third-generation detectors: the10 km
Einstein Telescope, and 40 km Cosmic Explorer. We have highlighted the main
technical challenges towards realizing the design, which requires dedicated
research programs. If demonstrated in current facilities, the techniques can be
transferred to new facilities with longer baselines.Comment: 14 pages, 15 figures, published versio
How to reuse a one-time pad and other notes on authentication, encryption and protection of quantum information
Quantum information is a valuable resource which can be encrypted in order to
protect it. We consider the size of the one-time pad that is needed to protect
quantum information in a number of cases. The situation is dramatically
different from the classical case: we prove that one can recycle the one-time
pad without compromising security. The protocol for recycling relies on
detecting whether eavesdropping has occurred, and further relies on the fact
that information contained in the encrypted quantum state cannot be fully
accessed. We prove the security of recycling rates when authentication of
quantum states is accepted, and when it is rejected. We note that recycling
schemes respect a general law of cryptography which we prove relating the size
of private keys, sent qubits, and encrypted messages. We discuss applications
for encryption of quantum information in light of the resources needed for
teleportation. Potential uses include the protection of resources such as
entanglement and the memory of quantum computers. We also introduce another
application: encrypted secret sharing and find that one can even reuse the
private key that is used to encrypt a classical message. In a number of cases,
one finds that the amount of private key needed for authentication or
protection is smaller than in the general case.Comment: 13 pages, improved rate of recycling proved in the case of rejection
of authenticatio
Bilinear noise subtraction at the GEO 600 observatory
We develop a scheme to subtract off bilinear noise from the gravitational wave strain data and demonstrate it at the GEO 600 observatory. Modulations caused by test mass misalignments on longitudinal control signals are observed to have a broadband effect on the mid-frequency detector sensitivity ranging from 50 Hz to 500 Hz. We estimate this bilinear coupling by making use of narrow-band signal injections that are already in place for noise projection purposes. A coherent bilinear signal is constructed by a two-stage system identification process where the involved couplings are approximated in terms of stable rational functions. The time-domain filtering efficiency is observed to depend upon the system identification process especially when the involved transfer functions cover a large dynamic range and have multiple resonant features. We improve upon the existing filter design techniques by employing a Bayesian adaptive directed search strategy that optimizes across the several key parameters that affect the accuracy of the estimated model. The resulting post-offline subtraction leads to a suppression of modulation side-bands around the calibration lines along with a broadband reduction of the mid-frequency noise floor. The filter coefficients are updated periodically to account for any non-stationarities that can arise within the coupling. The observed increase in the astrophysical range and a reduction in the occurrence of non-astrophysical transients suggest that the above method is a viable data cleaning technique for current and future gravitational wave observatories
Length sensing and control strategies for the LCGT interferometer
The optical readout scheme for the length degrees of freedom of the LCGT
interferometer is proposed. The control scheme is compatible both with the
broadband and detuned operations of the interferometer. Interferometer
simulations using a simulation software Optickle show that the sensing noise
couplings caused by the feedback control can be reduced below the target
sensitivity of LCGT with the use of feed forward. In order to improve the duty
cycle of the detector, a robust lock acquisition scheme using auxiliary lasers
will be used.Comment: 13 pages 9 figures. A proceedings paper for Amaldi9 conferenc
The next detectors for gravitational wave astronomy
This paper focuses on the next detectors for gravitational wave astronomy
which will be required after the current ground based detectors have completed
their initial observations, and probably achieved the first direct detection of
gravitational waves. The next detectors will need to have greater sensitivity,
while also enabling the world array of detectors to have improved angular
resolution to allow localisation of signal sources. Sect. 1 of this paper
begins by reviewing proposals for the next ground based detectors, and presents
an analysis of the sensitivity of an 8 km armlength detector, which is proposed
as a safe and cost-effective means to attain a 4-fold improvement in
sensitivity. The scientific benefits of creating a pair of such detectors in
China and Australia is emphasised. Sect. 2 of this paper discusses the high
performance suspension systems for test masses that will be an essential
component for future detectors, while sect. 3 discusses solutions to the
problem of Newtonian noise which arise from fluctuations in gravity gradient
forces acting on test masses. Such gravitational perturbations cannot be
shielded, and set limits to low frequency sensitivity unless measured and
suppressed. Sects. 4 and 5 address critical operational technologies that will
be ongoing issues in future detectors. Sect. 4 addresses the design of thermal
compensation systems needed in all high optical power interferometers operating
at room temperature. Parametric instability control is addressed in sect. 5.
Only recently proven to occur in Advanced LIGO, parametric instability
phenomenon brings both risks and opportunities for future detectors. The path
to future enhancements of detectors will come from quantum measurement
technologies. Sect. 6 focuses on the use of optomechanical devices for
obtaining enhanced sensitivity, while sect. 7 reviews a range of quantum
measurement options
Sub-SQL Sensitivity via Optical Rigidity in Advanced LIGO Interferometer with Optical Losses
The ``optical springs'' regime of the signal-recycled configuration of laser
interferometric gravitational-wave detectors is analyzed taking in account
optical losses in the interferometer arm cavities. This regime allows to obtain
sensitivity better than the Standard Quantum Limits both for a free test mass
and for a conventional harmonic oscillator. The optical losses restrict the
gain in sensitivity and achievable signal-to-noise ratio. Nevertheless, for
parameters values planned for the Advanced LIGO gravitational-wave detector,
this restriction is insignificant.Comment: 15 pages, 9 figure
Machine-learning nonstationary noise out of gravitational-wave detectors
Signal extraction out of background noise is a common challenge in high-precision physics experiments, where the measurement output is often a continuous data stream. To improve the signal-to-noise ratio of the detection, witness sensors are often used to independently measure background noises and subtract them from the main signal. If the noise coupling is linear and stationary, optimal techniques already exist and are routinely implemented in many experiments. However, when the noise coupling is nonstationary, linear techniques often fail or are suboptimal. Inspired by the properties of the background noise in gravitational wave detectors, this work develops a novel algorithm to efficiently characterize and remove nonstationary noise couplings, provided there exist witnesses of the noise source and of the modulation. In this work, the algorithm is described in its most general formulation, and its efficiency is demonstrated with examples from the data of the Advanced LIGO gravitational-wave observatory, where we could obtain an improvement of the detector gravitational-wave reach without introducing any bias on the source parameter estimation
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