754 research outputs found
Interaction of plane gravitational waves with a Fabry-Perot cavity in the local Lorentz frame
We analyze the interaction of plane '+'-polarized gravitational waves with a
Fabry-Perot cavity in the local Lorentz frame of the cavity input mirror
outside of the range of long-wave approximation with the force of radiation
pressure taken into account. The obtained detector response signal is
represented as a sum of two parts: (i) the phase shift due to displacement of
the movable mirror under the influence of gravitational wave and the force of
light pressure, and (ii) the phase shift due to direct interaction of
gravitational wave with light wave inside the cavity. We obtain formula for the
movable mirror law of motion paying close attention to the phenomena of optical
rigidity, radiative friction and direct coupling of gravitational wave to light
wave. Some issues concerning the detection of high-frequency gravitational
waves and the role of optical rigidity in it are discussed. We also examine in
detail special cases of optical resonance and small detuning from it and
compare our results with the known ones.Comment: 17 pages, 9 figures; corrected references [7,8,34], added 2 new
references (currently [35,36]), added comments on (i) relativistic
corrections, (ii) detector angular pattern, (iii) quantized electromagnetic
field, increased font in figure
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
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
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
Spectral Line Broadening and Angular Blurring due to Spacetime Geometry Fluctuations
We treat two possible phenomenological effects of quantum fluctuations of
spacetime geometry: spectral line broadening and angular blurring of the image
of a distance source. A geometrical construction will be used to express both
effects in terms of the Riemann tensor correlation function. We apply the
resulting expressions to study some explicit examples in which the fluctuations
arise from a bath of gravitons in either a squeezed state or a thermal state.
In the case of a squeezed state, one has two limits of interest: a coherent
state which exhibits classical time variation but no fluctuations, and a
squeezed vacuum state, in which the fluctuations are maximized.Comment: 21 pages, 2 figures. Dedicated to Raphael Sorkin on the occasion of
his 60th birthday. (v2: several references added and some minor errors
corrected
Conversion of conventional gravitational-wave interferometers into QND interferometers by modifying their input and/or output optics
The LIGO-II gravitational-wave interferometers (ca. 2006--2008) are designed
to have sensitivities at about the standard quantum limit (SQL) near 100 Hz.
This paper describes and analyzes possible designs for subsequent, LIGO-III
interferometers that can beat the SQL. These designs are identical to a
conventional broad-band interferometer (without signal recycling), except for
new input and/or output optics. Three designs are analyzed: (i) a
"squeezed-input interferometer" (conceived by Unruh based on earlier work of
Caves) in which squeezed vacuum with frequency-dependent (FD) squeeze angle is
injected into the interferometer's dark port; (ii) a "variational-output"
interferometer (conceived in a different form by Vyatchanin, Matsko and
Zubova), in which homodyne detection with FD homodyne phase is performed on the
output light; and (iii) a "squeezed-variational interferometer" with squeezed
input and FD-homodyne output. It is shown that the FD squeezed-input light can
be produced by sending ordinary squeezed light through two successive
Fabry-Perot filter cavities before injection into the interferometer, and
FD-homodyne detection can be achieved by sending the output light through two
filter cavities before ordinary homodyne detection. With anticipated technology
and with laser powers comparable to that planned for LIGO-II, these
interferometers can beat the amplitude SQL by factors in the range from 3 to 5,
corresponding to event rate increases between ~30 and ~100 over the rate for a
SQL-limited interferometer.Comment: Submitted to Physical Review D; RevTeX manuscript with 16 figures;
prints to 33 pages in Physical Review double column format. Minor revisions
have been made in response to referee repor
Zeno and Anti Zeno effect for a two level system in a squeezed bath
We discuss the appearance of Zeno (QZE) or anti-Zeno (QAE) effect in an
exponentially decaying system. We consider the quantum dynamics of a
continuously monitored two level system interacting with a squeezed bath. We
find that the behavior of the system depends critically on the way in which the
squeezed bath is prepared. For specific choices of the squeezing phase the
system shows Zeno or anti-Zeno effect in conditions for which it would decay
exponentially if no measurements were done. This result allows for a clear
interpretation in terms of the equivalent spin system interacting with a
fictitious magnetic field.Comment: 18 pages, 7 figures;added references for section 4;changes in the
nomenclatur
Quantum Limits in Space-Time Measurements
Quantum fluctuations impose fundamental limits on measurement and space-time
probing. Although using optimised probe fields can allow to push sensitivity in
a position measurement beyond the "standard quantum limit", quantum
fluctuations of the probe field still result in limitations which are
determined by irreducible dissipation mechanisms. Fluctuation-dissipation
relations in vacuum characterise the mechanical effects of radiation pressure
vacuum fluctuations, which lead to an ultimate quantum noise for positions. For
macroscopic reflectors, the quantum noise on positions is dominated by
gravitational vacuum fluctuations, and takes a universal form deduced from
quantum fluctuations of space-time curvatures in vacuum. These can be
considered as ultimate space-time fluctuations, fixing ultimate quantum limits
in space-time measurements.Comment: 11 pages, to appear in Quantum and Semiclassical Optic
QND measurement of a superconducting qubit in the weakly projective regime
Quantum state detectors based on switching of hysteretic Josephson junctions
biased close to their critical current are simple to use but have strong
back-action. We show that the back-action of a DC-switching detector can be
considerably reduced by limiting the switching voltage and using a fast
cryogenic amplifier, such that a single readout can be completed within 25 ns
at a repetition rate of 1 MHz without loss of contrast. Based on a sequence of
two successive readouts we show that the measurement has a clear quantum
non-demolition character, with a QND fidelity of 75 %.Comment: submitted to PR
Displacement- and Timing-Noise Free Gravitational-Wave Detection
Motivated by a recently-invented scheme of displacement-noise-free
gravitational-wave detection, we demonstrate the existence of
gravitational-wave detection schemes insusceptible to both displacement and
timing (laser) noises, and are thus realizable by shot-noise-limited laser
interferometry. This is possible due to two reasons: first, gravitational waves
and displacement disturbances contribute to light propagation times in
different manners; second, for an N-detector system, the number of signal
channels is of the order O(N^2), while the total number of timing- and
displacement-noise channels is of the order O(N).Comment: 4 pages, 3 figures; mistake correcte
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