Showing papers by "Karsten Danzmann published in 2008"

Observation of squeezed light with 10-dB quantum-noise reduction.

Abstract: Squeezing of light's quantum noise requires temporal rearranging of photons. This again corresponds to creation of quantum correlations between individual photons. Squeezed light is a nonclassical manifestation of light with great potential in high-precision quantum measurements, for example, in the detection of gravitational waves [C. M. Caves, Phys. Rev. D 23, 1693 (1981)]. Equally promising applications have been proposed in quantum communication [H. P. Yuen and J. H. Shapiro, IEEE Trans. Inf. Theory 24, 657 (1978)]. However, after 20 years of intensive research doubts arose whether strong squeezing can ever be realized as required for eminent applications. Here we show experimentally that strong squeezing of light's quantum noise is possible. We reached a benchmark squeezing factor of 10 in power (10 dB). Thorough analysis reveals that even higher squeezing factors will be feasible in our setup.

Search for gravitational waves from binary inspirals in S3 and S4 LIGO data

Abstract: We report on a search for gravitational waves from the coalescence of compact binaries during the third and fourth LIGO science runs. The search focused on gravitational waves generated during the inspiral phase of the binary evolution. In our analysis, we considered three categories of compact binary systems, ordered by mass: (i) primordial black hole binaries with masses in the range 0.35M_⊙

All-sky search for periodic gravitational waves in LIGO S4 data

Abstract: We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50–1000 Hz and with the frequency’s time derivative in the range −1×10^(−8) Hz s^(−1) to zero. Data from the fourth LIGO science run (S4) have been used in this search. Three different semicoherent methods of transforming and summing strain power from short Fourier transforms (SFTs) of the calibrated data have been used. The first, known as StackSlide, averages normalized power from each SFT. A “weighted Hough” scheme is also developed and used, which also allows for a multi-interferometer search. The third method, known as PowerFlux, is a variant of the StackSlide method in which the power is weighted before summing. In both the weighted Hough and PowerFlux methods, the weights are chosen according to the noise and detector antenna-pattern to maximize the signal-to-noise ratio. The respective advantages and disadvantages of these methods are discussed. Observing no evidence of periodic gravitational radiation, we report upper limits; we interpret these as limits on this radiation from isolated rotating neutron stars. The best population-based upper limit with 95% confidence on the gravitational-wave strain amplitude, found for simulated sources distributed isotropically across the sky and with isotropically distributed spin axes, is 4.28×10^(−24) (near 140 Hz). Strict upper limits are also obtained for small patches on the sky for best-case and worst-case inclinations of the spin axes.

Entanglement of macroscopic test masses and the Standard Quantum Limit in laser interferometry

Abstract: We show that the generation of entanglement of two heavily macroscopic mirrors is 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.

Search for gravitational-wave bursts from soft gamma repeaters

Abstract: We present a LIGO search for short-duration gravitational waves (GWs) associated with soft gamma ray repeater (SGR) bursts. This is the first search sensitive to neutron star f modes, usually considered the most efficient GW emitting modes. We find no evidence of GWs associated with any SGR burst in a sample consisting of the 27 Dec. 2004 giant flare from SGR 1806-20 and 190 lesser events from SGR 1806-20 and SGR 1900+14. The unprecedented sensitivity of the detectors allows us to set the most stringent limits on transient GW amplitudes published to date. We find upper limit estimates on the model-dependent isotropic GW emission energies (at a nominal distance of 10 kpc) between 3×1045 and 9×1052 erg depending on waveform type, detector antenna factors and noise characteristics at the time of the burst. These upper limits are within the theoretically predicted range of some SGR models.

Search for gravitational waves associated with 39 gamma-ray bursts using data from the second, third, and fourth LIGO runs

Abstract: We present the results of a search for short-duration gravitational-wave bursts associated with 39 gamma-ray bursts (GRBs) detected by gamma-ray satellite experiments during LIGO’s S2, S3, and S4 science runs. The search involves calculating the crosscorrelation between two interferometer data streams surrounding the GRB trigger time. We search for associated gravitational radiation from single GRBs, and also apply statistical tests to search for a gravitational-wave signature associated with the whole sample. For the sample examined, we find no evidence for the association of gravitational radiation with GRBs, either on a single-GRB basis or on a statistical basis. Simulating gravitational-wave bursts with sine-Gaussian waveforms, we set upper limits on the root-sum-square of the gravitational-wave strain amplitude of such waveforms at the times of the GRB triggers. We also demonstrate how a sample of several GRBs can be used collectively to set constraints on population models. The small number of GRBs and the significant change in sensitivity of the detectors over the three runs, however, limits the usefulness of a population study for the S2, S3, and S4 runs. Finally, we discuss prospects for the search sensitivity for the ongoing S5 run, and beyond for the next generation of detectors.

Stabilized lasers for advanced gravitational wave detectors

Abstract: Second generation gravitational wave detectors require high power lasers with more than 100 W of output power and with very low temporal and spatial fluctuations. To achieve the demanding stability levels required, low noise techniques and adequate control actuators have to be part of the high power laser design. In addition feedback control and passive noise filtering is used to reduce the fluctuations in the so-called prestabilized laser system (PSL). In this paper, we discuss the design of a 200 W PSL which is under development for the Advanced LIGO gravitational wave detector and will present the first results. The PSL noise requirements for advanced gravitational wave detectors will be discussed in general and the stabilization scheme proposed for the Advanced LIGO PSL will be described.

Search of S3 LIGO data for gravitational wave signals from spinning black hole and neutron star binary inspirals

Abstract: We report on the methods and results of the first dedicated search for gravitational waves emitted during the inspiral of compact binaries with spinning component bodies We analyze 788 hours of data collected during the third science run (S3) of the LIGO detectors We searched for binary systems using a detection template family specially designed to capture the effects of the spin-induced precession of the orbital plane We present details of the techniques developed to enable this search for spin-modulated gravitational waves, highlighting the differences between this and other recent searches for binaries with nonspinning components The template bank we employed was found to yield high matches with our spin-modulated target waveform for binaries with masses in the asymmetric range 10M⊙

DC-readout of a signal-recycled gravitational wave detector

Abstract: All first-generation large-scale gravitational wave detectors are operated at the dark fringe and use a heterodyne readout employing radio frequency (RF) modulation-demodulation techniques. However, the experience in the currently running interferometers reveals several problems connected with a heterodyne readout, of which phase noise of the RF modulation is the most serious one. A homodyne detection scheme (DC-readout), using the highly stabilized and filtered carrier light as local oscillator for the readout, is considered to be a favourable alternative. Recently a DC-readout scheme was implemented on the GEO 600 detector. We describe the results of first measurements and give a comparison of the performance achieved with homodyne and heterodyne readout. The implications of the combined use of DC-readout and signal-recycling are considered.

Double optical spring enhancement for gravitational wave detectors

Abstract: 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.

Astrophysically triggered searches for gravitational waves: status and prospects

Abstract: In gravitational-wave detection, special emphasis is put onto searches that focus on cosmic events detected by other types of astrophysical observatories. The astrophysical triggers, e.g. from γ-ray and x-ray satellites, optical telescopes and neutrino observatories, provide a trigger time for analyzing gravitational-wave data coincident with the event. In certain cases the expected frequency range, source energetics, directional and progenitor information are also available. Beyond allowing the recognition of gravitational waveforms with amplitudes closer to the noise floor of the detector, these triggered searches should also lead to rich science results even before the onset of Advanced LIGO. In this paper we provide a broad review of LIGO's astrophysically triggered searches and the sources they target.

Monolithic dielectric surfaces as new low-loss light-matter interfaces

Abstract: We propose a new mirror architecture, which is solely based upon structuring of the surface of a monolithic, possibly monocrystalline, bulk material. We found that a structure of T-shaped ridges of a subwavelength grating can theoretically provide 100% reflectivity. Since no material needs to be added to the mirror device, lowest mechanical loss can also be expected. Our approach might have compelling applications as a new light-matter interface.

First joint search for gravitational-wave bursts in LIGO and GEO 600 data

Abstract: We present the results of the first joint search for gravitational-wave bursts by the LIGO and GEO 600 detectors. We search for bursts with characteristic central frequencies in the band 768-2048 Hz in the data acquired between 22 February and 23 March, 2005 (fourth LSC Science Run-S4). We discuss the inclusion of the GEO 600 data in the Waveburst-CorrPower pipeline that first searches for coincident excess power events without taking into account differences in the antenna responses or strain sensitivities of the various detectors. We compare the performance of this pipeline to that of the coherent Waveburst pipeline based on the maximum likelihood statistic. This likelihood statistic is derived from a coherent sum of the detector data streams that takes into account the antenna patterns and sensitivities of the different detectors in the network. We find that the coherent Waveburst pipeline is sensitive to signals of amplitude 30-50% smaller than the Waveburst-CorrPower pipeline. We perform a search for gravitational-wave bursts using both pipelines and find no detection candidates in the S4 data set when all four instruments were operating stably.

A joint search for gravitational wave bursts with AURIGA and LIGO

Abstract: The first simultaneous operation of the AURIGA detector* and the LIGO observatory* was an opportunity to explore real data, joint analysis methods between two very different types of gravitational wave detectors: resonant bars and interferometers. This paper describes a coincident gravitational wave burst search, where data from the LIGO interferometers are cross-correlated at the time of AURIGA candidate events to identify coincident transients. The analysis pipeline is tuned with two thresholds, on the signal-to-noise ratio of AURIGA candidate events and on the significance of the cross-correlation test in LIGO. The false alarm rate is estimated by introducing time shifts between data sets and the network detection efficiency is measured by adding simulated gravitational wave signals to the detector output. The simulated waveforms have a significant fraction of power in the narrower AURIGA band. In the absence of a detection, we discuss how to set an upper limit on the rate of gravitational waves and to interpret it according to different source models. Due to the short amount of analyzed data and to the high rate of non-Gaussian transients in the detectors' noise at the time, the relevance of this study is methodological: this was the first joint search for gravitational wave bursts among detectors with such different spectral sensitivity and the first opportunity for the resonant and interferometric communities to unify languages and techniques in the pursuit of their common goal.

Optical ac coupling to overcome limitations in the detection of optical power fluctuations.

Abstract: A high-sensitivity detection method for optical power fluctuations is demonstrated based on photodetection in reflection of an optical resonator with a specific impedance matching. That resonator is used to reduce the carrier power reflected by the resonator while preserving the power fluctuation sidebands for frequencies above the resonator bandwidth. A sensitivity of 7 x 10(-10) Hz(-1/2) for relative power fluctuations was achieved with only 3 mA of detected photocurrent and 99.6% of the power remained for downstream experiments. As in the widely used ac coupling of electrical signals, this technique overcomes dynamic-range limits and reduces detector noise associated with large carrier amplitudes of the optical field.

Diffractive beam splitter characterization via a power-recycled interferometer

Abstract: We used the high-precision laser interferometer technique of power recycling to characterize the optical loss of an all-reflective grating beam splitter. This beam splitter was used to set up a Michelson interferometer with a power-recycling resonator with a finesse of 883. Analyzing the results obtained, we determined the beam splitter's total optical loss to be (0.193+/-0.019)%. Low loss all-reflective beam splitters might find application in future high-power laser interferometers for the detection of gravitational waves.

Creation of a quantum oscillator by classical control

Abstract: 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.

Subtraction of test mass angular noise in the LISA technology package interferometer

Abstract: When the position of a test mass in one dimension is measured with picometer accuracy, angular alignment jitter inevitably couples noise into the measurement. We present recent sensitivity measurements of the LISA technology package interferometer with articulated mirrors as test masses, actuated by piezo-electric transducers. The required longitudinal displacement resolution of 9 pm\(/\sqrt{\text{Hz}}\) above 3 mHz has been demonstrated with an angular noise that corresponds to the expected for on-orbit operation. The excess noise contribution of this test mass jitter onto the sensitive displacement readout was completely subtracted by fitting the angular interferometric data streams to the longitudinal displacement measurement. Thus, this cross-coupling constitutes no limitation to the required performance of the LISA technology package interferometry.

Switching from "absorption within transparency" to "transparency within transparency" in an electromagnetically induced absorption dominated transition.

Abstract: The absorption of a resonant coupling laser driving a closed degenerate two-level system in an atomic cesium beam was investigated as a function of the detuning of a second laser probing the same transition. The measurements were performed for four different polarization combinations of the two laser beams. Except for the beams of counterrotating polarizations all coupling-laser absorption profiles showed “absorption within transparency,” i.e., the absorption in the region around the two-photon resonance was smaller than the absorption corresponding to the one-photon transition induced by the coupling laser, and an extra absorption peak was observed on this curve at the two-photon resonance. With regard to the beams of counterrotating polarizations we observed a switch from absorption within transparency to “transparency within transparency” when the probe-laser power exceeded the constant coupling-laser power. In other words, the cesium ensemble became mostly transparent to the coupling-laser beam at the two-photon resonance.

Upper limit map of a background of gravitational waves (Physical Review D - Particles, Fields, Gravitation and Cosmology (2007) 76, (082003))

Abstract: This paper was published online on 29 October 2007 with a formatting error in the fiftieth affiliation in the author list.The affiliation should read as ‘‘University of Western Australia, Crawley, WA 6009, Australia.’’ The affiliation has beencorrected as of 4 March 2008. The affiliation is incorrect in the printed version of the journal.

Opto-mechanical frequency shifting of scattered light

Abstract: Light being scattered back from external surfaces or optical components can affect the sensitivity of optical measurement systems such as interferometers. By modulating the optical path length in front of a critical optical component the noise contributions due to the scattered light can be shifted out of the frequency band of interest. An opto-mechanical phase shifter has been designed for this purpose and noise reduction has been demonstrated.

Giant Kerr effect in closed degenerate two-level transitions

Abstract: Extremely large optical Kerr non-linearities (n2) and (n4) were measured in two closed degenerate two-level transitions in the caesium D2 line when a probe and a coupling laser simultaneously probed and coupled the hyperfine structure in an atomic beam. The magnitude of the measured non-linearities in both transitions were found to be a function of the coupling laser intensity and of the probe detuning from the two-photon resonance. In a figure of merit, the ratio between the non-unitarian part of the refractive index and the absorption coefficient measured in conditions of electromagnetically induced transparency showed a maximum value for a probe detuning of 160 kHz from the two-photon resonance and resulted in being 105 times larger than in the absence of the coupling laser field.

100% reflectivity from a monolithic dielectric microstructured surface

Abstract: Here, we propose a new mirror architecture which is solely based upon a monolithic dielectric micro-structured surface. Hence, the mirror device, which consists of a possibly mono-crystalline bulk material, can in principle simultaneously provide perfect reflectivity and lowest mechanical loss. By specifically structuring the monolithic surface, resulting in T-shaped ridges of a subwavelength grating, a resonant behavior of light coupling can be realized, leading to theoretically 100% reflectivity.

Switch of absorption in coherently driven media

Abstract: A system usually characterized by electromagnetically induced absorption was investigated with a probe and a coupling laser. Properly tuning the laser polarizations and intensities, inversions in the lasers absorption were measured for the first time.

Power-recycled michelson interferometer with a 50/50 grating beam splitter

Abstract: We designed and fabricated an all-reflective 50/50 beam splitter based on a dielectric grating. This beam splitter was used to set up a power-recycled Michelson interferometer with a finesse of about FPR ≈ 880. Aspects of the diffractive beam splitter as well as of the interferometer design are discussed.

Inversion of the Coupling Absorption at the Two-Photon Resonance in a Coupling-Probe-Spectroscopy Experiment

Abstract: After the discovery of electromagnetically induced absorption (EIA), both theoretical and experimental research was performed to explain not only the probe laser absorption and dispersion spectra, but also those of the coupling laser. The investigations of EIA in degenerate two-level systems have often been realized using two linearly polarized lasers of orthogonal polarization [1]. However, the simplest configuration leading to EIA is the so-called N-system [2] which basically requires the simultaneous adoption of a circularly polarized coupling laser and a linearly polarized probe (here called σ−π). To our knowledge, no experimental measurements of the coupling laser exist in the configurations (σ+−σ−, π−σ− or σ+−π).

Experimental Comparison between the Index of Refraction in Strongly Driven and Degenerate Two-Level Systems

Abstract: Negative dispersion and transparency in a strongly driven calcium two-level system and positive dispersion and transparency or anomalous dispersion and enhanced absorption in closed degenerate two-level systems in caesium have been observed using pump-probe spectroscopy.

Comparative study of index of refraction: The strongly driven and the degenerate two-level systems

Abstract: This study compares the experimental results of absorption and refractive index of a probe laser measured in a strongly driven two-level atom with the results measured in a degenerate two-level system using pump-probe spectroscopy. This work demonstrates the possibility of realization an anomalous dispersive transparent medium using the strongly driven 4s2 1S0 - 4s4p 1P1 Ca transition. Absorption and phase shift profiles are measured as function of the driving field intensity using a Ca atomic beam. With increasing driving field intensities absorption and phase shift decrease, but the absorption decreases stronger than the dispersion. Results show that the resonant absorption and the anomalous dispersion are reduced with respect to the non-driving case by a factor 490 and 47, respectively. This means that a ~ 10-fold enhancement of the amount of dispersion provided per amount of absorption is attained.