8 research outputs found
Energetic Quantum Limit in Large-Scale Interferometers
For each optical topology of an interferometric gravitational wave detector,
quantum mechanics dictates a minimum optical power (the ``energetic quantum
limit'') to achieve a given sensitivity. For standard topologies, when one
seeks to beat the standard quantum limit by a substantial factor, the energetic
quantum limit becomes impossibly large. Intracavity readout schemes may do so
with manageable optical powers.Comment: Revised version; to be published in Proceedings of the 1999 Edoardo
Amaldi Conference on Gravitational Waves; 11 pages including figures;
manuscript is RevTex; figures are .eps; an AIP style file is include
Dual-Resonator Speed Meter for a Free Test Mass
A description and analysis are given of a ``speed meter'' for monitoring a
classical force that acts on a test mass. This speed meter is based on two
microwave resonators (``dual resonators''), one of which couples evanescently
to the position of the test mass. The sloshing of the resulting signal between
the resonators, and a wise choice of where to place the resonators' output
waveguide, produce a signal in the waveguide that (for sufficiently low
frequencies) is proportional to the test-mass velocity (speed) rather than its
position. This permits the speed meter to achieve force-measurement
sensitivities better than the standard quantum limit (SQL), both when operating
in a narrow-band mode and a wide-band mode. A scrutiny of experimental issues
shows that it is feasible, with current technology, to construct a
demonstration speed meter that beats the wide-band SQL by a factor 2. A concept
is sketched for an adaptation of this speed meter to optical frequencies; this
adaptation forms the basis for a possible LIGO-III interferometer that could
beat the gravitational-wave standard quantum limit h_SQL, but perhaps only by a
factor 1/xi = h_SQL/h ~ 3 (constrained by losses in the optics) and at the
price of a very high circulating optical power --- larger by 1/xi^2 than that
required to reach the SQL.Comment: RevTex: 13 pages with 4 embedded figures (two .eps format and two
drawn in TeX); Submitted to Physical Review
The noise in gravitational-wave detectors and other classical-force measurements is not influenced by test-mass quantization
It is shown that photon shot noise and radiation-pressure back-action noise
are the sole forms of quantum noise in interferometric gravitational wave
detectors that operate near or below the standard quantum limit, if one filters
the interferometer output appropriately. No additional noise arises from the
test masses' initial quantum state or from reduction of the test-mass state due
to measurement of the interferometer output or from the uncertainty principle
associated with the test-mass state. Two features of interferometers are
central to these conclusions: (i) The interferometer output (the photon number
flux N(t) entering the final photodetector) commutes with itself at different
times in the Heisenberg Picture, [N(t), N(t')] = 0, and thus can be regarded as
classical. (ii) This number flux is linear in the test-mass initial position
and momentum operators x_o and p_o, and those operators influence the measured
photon flux N(t) in manners that can easily be removed by filtering -- e.g., in
most interferometers, by discarding data near the test masses' 1 Hz swinging
freqency. The test-mass operators x_o and p_o contained in the unfiltered
output N(t) make a nonzero contribution to the commutator [N(t), N(t')]. That
contribution is cancelled by a nonzero commutation of the photon shot noise and
radiation-pressure noise, which also are contained in N(t). This cancellation
of commutators is responsible for the fact that it is possible to derive an
interferometer's standard quantum limit from test-mass considerations, and
independently from photon-noise considerations. These conclusions are true for
a far wider class of measurements than just gravitational-wave interferometers.
To elucidate them, this paper presents a series of idealized thought
experiments that are free from the complexities of real measuring systems.Comment: Submitted to Physical Review D; Revtex, no figures, prints to 14
pages. Second Revision 1 December 2002: minor rewording for clarity,
especially in Sec. II.B.3; new footnote 3 and passages before Eq. (2.35) and
at end of Sec. III.B.
Ultra-smooth lithium niobate photonic micro-structures by surface tension reshaping
Annealing of micro-structured lithium niobate substrates at temperatures close to, but below the melting point, allows surface tension to reshape preferentially melted surface zones of the crystal. The reshaped surface re-crystallizes upon cooling to form a single crystal again as it is seeded by the bulk which remains solid throughout the process. This procedure yields ultra-smooth single crystal superstructures suitable for the fabrication of photonic micro-components with low scattering loss
First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data
International audienceSpinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signal-to-noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11Â pulsars using data from Advanced LIGOâs first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far
Search for intermediate mass black hole binaries in the first observing run of Advanced LIGO
International audienceDuring their first observational run, the two Advanced LIGO detectors attained an unprecedented sensitivity, resulting in the first direct detections of gravitational-wave signals produced by stellar-mass binary black hole systems. This paper reports on an all-sky search for gravitational waves (GWs) from merging intermediate mass black hole binaries (IMBHBs). The combined results from two independent search techniques were used in this study: the first employs a matched-filter algorithm that uses a bank of filters covering the GW signal parameter space, while the second is a generic search for GW transients (bursts). No GWs from IMBHBs were detected; therefore, we constrain the rate of several classes of IMBHB mergers. The most stringent limit is obtained for black holes of individual mass 100ââMâ, with spins aligned with the binary orbital angular momentum. For such systems, the merger rate is constrained to be less than 0.93ââGpcâ3âyrâ1 in comoving units at the 90%Â confidence level, an improvement of nearly 2 orders of magnitude over previous upper limits
First low-frequency Einstein@Home all-sky search for continuous gravitational waves in Advanced LIGO data
International audienceWe report results of a deep all-sky search for periodic gravitational waves from isolated neutron stars in data from the first Advanced LIGO observing run. This search investigates the low frequency range of Advanced LIGO data, between 20 and 100Â Hz, much of which was not explored in initial LIGO. The search was made possible by the computing power provided by the volunteers of the Einstein@Home project. We find no significant signal candidate and set the most stringent upper limits to date on the amplitude of gravitational wave signals from the target population, corresponding to a sensitivity depth of 48.7ââ[1/Hz]. At the frequency of best strain sensitivity, near 100Â Hz, we set 90% confidence upper limits of 1.8Ă10-25. At the low end of our frequency range, 20Â Hz, we achieve upper limits of 3.9Ă10-24. At 55Â Hz we can exclude sources with ellipticities greater than 10-5 within 100Â pc of Earth with fiducial value of the principal moment of inertia of 1038ââkgâm2