864 research outputs found
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
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
Phase diffusion pattern in quantum nondemolition systems
We quantitatively analyze the dynamics of the quantum phase distribution
associated with the reduced density matrix of a system, as the system evolves
under the influence of its environment with an energy-preserving quantum
nondemolition (QND) type of coupling. We take the system to be either an
oscillator (harmonic or anharmonic) or a two-level atom (or equivalently, a
spin-1/2 system), and model the environment as a bath of harmonic oscillators,
initially in a general squeezed thermal state. The impact of the different
environmental parameters is explicitly brought out as the system starts out in
various initial states. The results are applicable to a variety of physical
systems now studied experimentally with QND measurements.Comment: 18 pages, REVTeX, 8 figure
Quantum Signatures of the Optomechanical Instability
In the past few years, coupling strengths between light and mechanical motion
in optomechanical setups have improved by orders of magnitude. Here we show
that, in the standard setup under continuous laser illumination, the steady
state of the mechanical oscillator can develop a non-classical, strongly
negative Wigner density if the optomechanical coupling is large at the
single-photon level. Because of its robustness, such a Wigner density can be
mapped using optical homodyne tomography. These features are observed near the
onset of the instability towards self-induced oscillations. We show that there
are also distinct signatures in the photon-photon correlation function
in that regime, including oscillations decaying on a time scale
not only much longer than the optical cavity decay time, but even longer than
the \emph{mechanical} decay time.Comment: 6 pages including 1 appendix. 6 Figures. Correcte
Optical noise correlations and beating the standard quantum limit in advanced gravitational-wave detectors
The uncertainty principle, applied naively to the test masses of a
laser-interferometer gravitational-wave detector, produces a Standard Quantum
Limit (SQL) on the interferometer's sensitivity. It has long been thought that
beating this SQL would require a radical redesign of interferometers. However,
we show that LIGO-II interferometers, currently planned for 2006, can beat the
SQL by as much as a factor two over a bandwidth \Delta f \sim f, if their
thermal noise can be pushed low enough. This is due to dynamical correlations
between photon shot noise and radiation-pressure noise, produced by the LIGO-II
signal-recycling mirror.Comment: 12 pages, 2 figures; minor changes, some references adde
Quantum-Limited Position Detection and Amplification: A Linear Response Perspective
Using standard linear response relations, we derive the quantum limit on the
sensitivity of a generic linear-response position detector, and the noise
temperature of a generic linear amplifier. Particular emphasis is placed on the
detector's effective temperature and damping effects; the former quantity
directly determines the dimensionless power gain of the detector. Unlike the
approach used in the seminal work of Caves [Phys. Rev. D, 26, 1817 (1982)], the
linear-response approach directly involves the noise properties of the
detector, and allows one to derive simple necessary and sufficient conditions
for reaching the quantum limit. Our results have direct relevance to recent
experiments on nanoelectromechanical systems, and complement recent theoretical
studies of particular mesoscopic position detectors.Comment: 9 pages; minor typos correcte
QND and higher order effects for a nonlinear meter in an interferometric gravitational wave antenna
A new optical topology and signal readout strategy for a laser interferometer
gravitational wave detector were proposed recently by Braginsky and Khalili .
Their method is based on using a nonlinear medium inside a microwave oscillator
to detect the gravitational-wave-induced spatial shift of the interferometer's
standing optical wave. This paper proposes a quantum nondemolition (QND) scheme
that could be realistically used for such a readout device and discusses a
"fundamental" sensitivity limit imposed by a higher order optical effect.Comment: LaTex, 17 pages, 3 figure
Quantum measurements and Paul traps in gravitational backgrounds
In the present work we solve the motion equations of a particle in a Paul
trap embeded in the gravitational field of a spherically symmetric mass. One of
the ideas behind this work concerns the analysis of the effects that the
gravity--induced quantum noise, stemming from the bodies in the neighborhood of
the Paul trap, could have upon the enhancement of the quantum behavior of this
system. This will be done considering a series expansion for the gravitational
field of the source, and including in the Hamiltonian of the Paul trap only the
first two terms. Higher--order contributions will be introduced as part of the
environment of the system, and in consequence will not appear in the
Hamiltonian. In other words, we put forward an argument that allows us to
differentiate those gravitational degrees of freedom that will appear as an
uncontrollable influence on the Paul trap. Along the ideas of the so called
restricted path integral formalism, we take into account the continuous
monitoring of the position of our particle, and in consequence the
corresponding propagators and probabilities, associated with the different
measurements outputs, are obtained.
Afterwards, the differential equation related to a quantum nondemolition
variable is posed and solved, i.e., a family of quantum nondemolition
parameters is obtained. Finally, a qualitative analysis of the effects on the
system, of the gravity--induced environment, will be done.Comment: Accepted in International Journal of Modern Physics
Cooling of a micro-mechanical oscillator using radiation pressure induced dynamical back-action
Cooling of a 58 MHz micro-mechanical resonator from room temperature to 11 K
is demonstrated using cavity enhanced radiation pressure. Detuned pumping of an
optical resonance allows enhancement of the blue shifted motional sideband
(caused by the oscillator's Brownian motion) with respect to the red-shifted
sideband leading to cooling of the mechanical oscillator mode. The reported
cooling mechanism is a manifestation of the effect of radiation pressure
induced dynamical backaction. These results constitute an important step
towards achieving ground state cooling of a mechanical oscillator.Comment: accepted for publication (Phys. Rev. Lett.
Forced and self-excited oscillations of an optomechanical cavity
We experimentally study forced and self oscillations of an optomechanical
cavity which is formed between a fiber Bragg grating that serves as a static
mirror and between a freely suspended metallic mechanical resonator that serves
as a moving mirror. In the domain of small amplitude mechanical oscillations,
we find that the optomechanical coupling is manifested as changes in the
effective resonance frequency, damping rate and cubic nonlinearity of the
mechanical resonator. Moreover, self oscillations of the micromechanical mirror
are observed above a certain optical power threshold. A comparison between the
experimental results and a theoretical model that we have recently presented
yields a good agreement. The comparison also indicates that the dominant
optomechanical coupling mechanism is the heating of the metallic mirror due to
optical absorption.Comment: 11 pages, 6 figure
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