23 research outputs found
Local readout enhancement for detuned signal-recycling interferometers
Motivated by the optical-bar scheme of Braginsky, Gorodetsky and Khalili, we
propose to add to a high power detuned signal-recycling interferometer a local
readout scheme which measures the motion of the arm-cavity front mirror. At low
frequencies this mirror moves together with the arm-cavity end mirror, under
the influence of gravitational waves. This scheme improves the low-frequency
quantum-noise-limited sensitivity of optical-spring interferometers
significantly and can be considered as a incorporation of the optical-bar
scheme into currently planned second-generation interferometers. On the other
hand it can be regarded as an extension of the optical bar scheme. Taking
compact-binary inspiral signals as an example, we illustrate how this scheme
can be used to improve the sensitivity of the planned Advanced LIGO
interferometer, in various scenarios, using a realistic classical-noise budget.
We also discuss how this scheme can be implemented in Advanced LIGO with
relative ease
Double optical spring enhancement for gravitational-wave detectors
Currently planned second-generation gravitational-wave laser interferometers such as Advanced LIGO exploit the extensively investigated signal-recycling technique. Candidate Advanced LIGO configurations are usually designed to have two resonances within the detection band, around which the sensitivity is enhanced: a stable optical resonance and an unstable optomechanical resonance—which is upshifted from the pendulum frequency due to the so-called optical-spring effect. As an alternative to a feedback control system, we propose an all-optical stabilization scheme, in which a second optical spring is employed, and the test mass is trapped by a stable ponderomotive potential well induced by two carrier light fields whose detunings have opposite signs. The double optical spring also brings additional flexibility in reshaping the noise spectral density and optimizing toward specific gravitational-wave sources. The presented scheme can be extended easily to a multi-optical-spring system that allows further optimization
Creation of a quantum oscillator by classical control
As a pure quantum state is being approached via linear feedback, and the
occupation number approaches and eventually goes below unity, optimal control
becomes crucial. We obtain theoretically the optimal feedback controller that
minimizes the uncertainty for a general linear measurement process, and show
that even in the absence of classical noise, a pure quantum state is not always
achievable via feedback. For Markovian measurements, the deviation from minimum
Heisenberg Uncertainty is found to be closely related to the extent to which
the device beats the free-mass Standard Quantum Limit for force measurement. We
then specialize to optical Markovian measurements, and demonstrate that a
slight modification to the usual input-output scheme -- either injecting
frequency independent squeezed vacuum or making a homodyne detection at a
non-phase quadrature -- allows controlled states of kilogram-scale mirrors in
future LIGO interferometers to reach occupation numbers significantly below
unity.Comment: 4 pages, 2 figure
Entanglement of macroscopic test masses and the Standard Quantum Limit in laser interferometry
We show that the generation of entanglement of two heavily macroscopic
mirrors with masses of up to several kilograms are feasible with state of the
art techniques of high-precision laser interferometry. The basis of such a
demonstration would be a Michelson interferometer with suspended mirrors and
simultaneous homodyne detections at both interferometer output ports. We
present the connection between the generation of entanglement and the Standard
Quantum Limit (SQL) for a free mass. The SQL is a well-known reference limit in
operating interferometers for gravitational-wave detection and provides a
measure of when macroscopic entanglement can be observed in the presence of
realistic decoherence processes
Quantum state preparation and macroscopic entanglement in gravitational-wave detectors
Long-baseline laser-interferometer gravitational-wave detectors are operating
at a factor of 10 (in amplitude) above the standard quantum limit (SQL) within
a broad frequency band. Such a low classical noise budget has already allowed
the creation of a controlled 2.7 kg macroscopic oscillator with an effective
eigenfrequency of 150 Hz and an occupation number of 200. This result, along
with the prospect for further improvements, heralds the new possibility of
experimentally probing macroscopic quantum mechanics (MQM) - quantum mechanical
behavior of objects in the realm of everyday experience - using
gravitational-wave detectors. In this paper, we provide the mathematical
foundation for the first step of a MQM experiment: the preparation of a
macroscopic test mass into a nearly minimum-Heisenberg-limited Gaussian quantum
state, which is possible if the interferometer's classical noise beats the SQL
in a broad frequency band. Our formalism, based on Wiener filtering, allows a
straightforward conversion from the classical noise budget of a laser
interferometer, in terms of noise spectra, into the strategy for quantum state
preparation, and the quality of the prepared state. Using this formalism, we
consider how Gaussian entanglement can be built among two macroscopic test
masses, and the performance of the planned Advanced LIGO interferometers in
quantum-state preparation
Searching for a Stochastic Background of Gravitational Waves with LIGO
The Laser Interferometer Gravitational-wave Observatory (LIGO) has performed
the fourth science run, S4, with significantly improved interferometer
sensitivities with respect to previous runs. Using data acquired during this
science run, we place a limit on the amplitude of a stochastic background of
gravitational waves. For a frequency independent spectrum, the new limit is
. This is currently the most sensitive
result in the frequency range 51-150 Hz, with a factor of 13 improvement over
the previous LIGO result. We discuss complementarity of the new result with
other constraints on a stochastic background of gravitational waves, and we
investigate implications of the new result for different models of this
background.Comment: 37 pages, 16 figure
Translational models for vascular cognitive impairment: a review including larger species.
BACKGROUND: Disease models are useful for prospective studies of pathology, identification of molecular and cellular mechanisms, pre-clinical testing of interventions, and validation of clinical biomarkers. Here, we review animal models relevant to vascular cognitive impairment (VCI). A synopsis of each model was initially presented by expert practitioners. Synopses were refined by the authors, and subsequently by the scientific committee of a recent conference (International Conference on Vascular Dementia 2015). Only peer-reviewed sources were cited. METHODS: We included models that mimic VCI-related brain lesions (white matter hypoperfusion injury, focal ischaemia, cerebral amyloid angiopathy) or reproduce VCI risk factors (old age, hypertension, hyperhomocysteinemia, high-salt/high-fat diet) or reproduce genetic causes of VCI (CADASIL-causing Notch3 mutations). CONCLUSIONS: We concluded that (1) translational models may reflect a VCI-relevant pathological process, while not fully replicating a human disease spectrum; (2) rodent models of VCI are limited by paucity of white matter; and (3) further translational models, and improved cognitive testing instruments, are required