3,354 research outputs found
Gravitational wave detectors: Squeezing up the sensitivity
Gravitational wave detectors based on laser interferometry have reached an incredible level of sensitivity. But to develop to the level needed to explore the Universe, the next generation of detectors will probably need to use squeezed light
Elastic Lennard-Jones Polymers Meet Clusters -- Differences and Similarities
We investigate solid-solid and solid-liquid transitions of elastic flexible
off-lattice polymers with Lennard-Jones monomer-monomer interaction and
anharmonic springs by means of sophisticated variants of multicanonical Monte
Carlo methods. We find that the low-temperature behavior depends strongly and
non-monotonically on the system size and exhibits broad similarities to unbound
atomic clusters. Particular emphasis is dedicated to the classification of
icosahedral and non-icosahedral low-energy polymer morphologies.Comment: 9 pages, 17 figure
Cryogenic Q-factor measurement of optical substrates for optimization of gravitational wave detectors
Future generations of gravitational wave interferometers are likely to be operated at cryogenic temperatures because one of the sensitivity limiting factors of the present generation is the thermal noise of end mirrors and beam splitters that occurs in the optical substrates as well as in the dielectric coatings. A possible method for minimizing thermal noise is cooling to cryogenic temperatures, maximizing the mechanical quality factor Q, and maximizing the eigenfrequencies of the substrate. We present experimental details of a new cryogenic apparatus that is suitable for the measurement of the temperature-dependent Q-factor of reflective, transmissive as well as nano-structured grating optics down to 5 K. In particular, the SQUID-based and the optical interferometric approaches to the measurement of the amplitude of vibrating test bodies are compared and the method of ring-down recording is described
Input-output relations for a 3-port grating coupled Fabry-Perot cavity
We analyze an optical 3-port reflection grating by means of a scattering
matrix formalism. Amplitude and phase relations between the 3 ports, i.e. the 3
orders of diffraction are derived. Such a grating can be used as an
all-reflective, low-loss coupler to Fabry-Perot cavities. We derive the input
output relations of a 3-port grating coupled cavity and find distinct
properties not present in 2-port coupled cavities. The cavity relations further
reveal that the 3-port coupler can be designed such that the additional cavity
port interferes destructively. In this case the all-reflective, low-loss,
single-ended Fabry-Perot cavity becomes equivalent to a standard transmissive,
2-port coupled cavity
Demonstration of 3-port grating phase relations
We experimentally demonstrate the phase relations of 3-port gratings by
investigating 3-port coupled Fabry-Perot cavities. Two different gratings which
have the same 1st order diffraction efficiency but differ substantially in
their 2nd order diffraction efficiency have been designed and manufactured.
Using the gratings as couplers to Fabry-Perot cavities we could validate the
results of an earlier theoretical description of the phases at a three port
grating
Changes in union membership over time : a panel analysis for West Germany
Despite the apparent stability of the wage bargaining institutions in West Germany, aggregate union membership has been declining dramatically since the early 90's. However, aggregate gross membership numbers do not distinguish by employment status and it is impossible to disaggregate these sufficiently. This paper uses four waves of the German Socioeconomic Panel in 1985, 1989, 1993, and 1998 to perform a panel analysis of net union membership among employees. We estimate a correlated random effects probit model suggested in Chamberlain (1984) to take proper account of individual specfic effects. Our results suggest that at the individual level the propensity to be a union member has not changed considerably over time. Thus, the aggregate decline in membership is due to composition effects. We also use the estimates to predict net union density at the industry level based on the IAB employment subsample for the time period 1985 to 1997. JEL - Klassifikation: J
The Gouy phase shift in nonlinear interactions of waves
We theoretically analyze the influence of the Gouy phase shift on the nonlinear interaction between waves of different frequencies. We focus on interaction of optical fields, e.g. through birefringent crystals, and show that focussing, stronger than suggested by the Boyd-Kleinman factor, can further improve nonlinear processes. An increased value of 3.32 for the optimal focussing parameter for a single pass process is found. The new value builds on the compensation of the Gouy phase shift by a spatially varying, instead constant, wave vector phase mismatch. We analyze the single-ended, singly resonant standing wave nonlinear cavity and show that in this case the Gouy phase shift leads to an additional phase during backreflection. Our numerical simulations may explain ill-understood experimental observations in such devices
Preparing the bound instance of quantum entanglement
Among the possibly most intriguing aspects of quantum entanglement is that it
comes in "free" and "bound" instances. Bound entangled states require entangled
states in preparation but, once realized, no free entanglement and therefore no
pure maximally entangled pairs can be regained. Their existence hence certifies
an intrinsic irreversibility of entanglement in nature and suggests a
connection with thermodynamics. In this work, we present a first experimental
unconditional preparation and detection of a bound entangled state of light. We
consider continuous-variable entanglement, use convex optimization to identify
regimes rendering its bound character well certifiable, and realize an
experiment that continuously produced a distributed bound entangled state with
an extraordinary and unprecedented significance of more than ten standard
deviations away from both separability and distillability. Our results show
that the approach chosen allows for the efficient and precise preparation of
multimode entangled states of light with various applications in quantum
information, quantum state engineering and high precision metrology.Comment: The final version accounts for a recent comment in Nature Physics
[24] clarifying that a previous claim of having generated bound entanglement
[23] was not supported by the authors' data. We also extended our
introduction and discussion and also added reference
PHYLOGENY OF THE ARCHAEBACTERIA AND EUKARYOTES: HOMOLOGY OF THE DNA-DEPENDENT RNA POLYMERASES
First Long-Term Application of Squeezed States of Light in a Gravitational-Wave Observatory
We report on the first long-term application of squeezed vacuum states of
light to improve the shot-noise-limited sensitivity of a gravitational-wave
observatory. In particular, squeezed vacuum was applied to the German/British
detector GEO600 during a period of three months from June to August 2011, when
GEO600 was performing an observational run together with the French/Italian
Virgo detector. In a second period squeezing application continued for about 11
months from November 2011 to October 2012. During this time, squeezed vacuum
was applied for 90.2% (205.2 days total) of the time that science-quality data
was acquired with GEO600. Sensitivity increase from squeezed vacuum application
was observed broad-band above 400Hz. The time average of gain in sensitivity
was 26% (2.0dB), determined in the frequency band from 3.7kHz to 4.0kHz. This
corresponds to a factor of two increase in observed volume of the universe, for
sources in the kHz region (e.g. supernovae, magnetars). We introduce three new
techniques to enable stable long-term application of squeezed light, and show
that the glitch-rate of the detector did not increase from squeezing
application. Squeezed vacuum states of light have arrived as a permanent
application, capable of increasing the astrophysical reach of
gravitational-wave detectors.Comment: 4 pages, 4 figure
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