Laser Interferometer Gravitational-Wave Observatory

Le Laser Interferometer Gravitational-Wave Observatory (« Observatoire d'ondes gravitationnelles par interférométrie laser »), en abrégé LIGO, est une expérience de physique à grande échelle dont le but est de détecter directement les ondes gravitationnelles. Cofondé en 1992 par Kip Thorne et Ronald Drever du Caltech et Rainer Weiss du MIT, le LIGO est un projet conjoint entre les scientifiques du MIT, du Caltech et de nombreuses autres institutions et universités. L'analyse des données astronomiques sur les ondes gravitationnelles est à la charge du LIGO Scientific Collaboration (LSC) qui regroupe 900 scientifiques dans le monde. LIGO est financé par la National Science Foundation (NSF), avec des contributions importantes du UK Science and Technology Facilities Council (Royaume-Uni), de la Société Max-Planck (Allemagne) et de l'Australian Research Council (Australie). À la mi-, le plus grand centre mondial sur les ondes gravitationnelles devrait terminer une rénovation complète de

Challenges and opportunities of gravitational-wave searches at MHz to GHz frequencies

Valerie Fiona Domcke, Daniel Garcia Figueroa, Francisco Torrenti

The first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This white paper outlines the challenges and gains expected in gravitational-wave searches at frequencies above the LIGO/Virgo band, with a particular focus on Ultra High-Frequency Gravitational Waves (UHF-GWs), covering the MHz to GHz range. The absence of known astrophysical sources in this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of the most promising gravitational sources. We review several detector concepts that have been proposed to take up this challenge, and compare their expected sensitivity with the signal strength predicted in various models. This report is the summary of the workshop "Challenges and opportunities of high-frequency gravitational wave detection" held at ICTP Trieste, Italy in October 2019, that set up the stage for the recently launched Ultra-High-Frequency Gravitational Wave (UHF-GW) initiative.

SPRINGER INT PUBL AG2021

Ability of LIGO and LISA to probe the equation of state of the early Universe

Daniel Garcia Figueroa

The expansion history of the Universe between the end of inflation and the onset of radiation-domination (RD) is currently unknown. If the equation of state during this period is stiffer than that of radiation, w > 1/3, the gravitational wave (GW) background from inflation acquires a blue-tilt d log rho GW/d log f = 2(w-1/3)/(w+1/3) > 0 at frequencies f >> f(RD) corresponding to modes re-entering the horizon during the stiff-domination (SD), where f(RD) is the frequency today of the horizon scale at the SD-to-RD transition. We characterized in detail the transfer function of the GW energy density spectrum, considering both 'instant' and smooth modelings of the SD-to-RD transition. The shape of the spectrum is controlled by w, f(RD), and H-inf (the Hubble scale of inflation). We determined the parameter space compatible with a detection of this signal by LIGO and LISA, including possible changes in the number of relativistic degrees of freedom, and the presence of a tensor tilt. Consistency with upper bounds on stochastic GW backgrounds, however, rules out a significant fraction of the observable parameter space. We find that this renders the signal unobservable by Advanced LIGO, in all cases. The GW background remains detectable by LISA, though only in a small island of parameter space, corresponding to scenarios with an equation of state in the range 0.46 less than or similar to w less than or similar to 0.56 and a high inflationary scale H-inf greater than or similar to 10(13) GeV, but low reheating temperature 1 MeV less than or similar to T-RD less than or similar to 150 MeV (equivalently, 10(-11) Hz less than or similar to f(RD) less than or similar to 3.6.10(-9) Hz). Implications for early Universe scenarios resting upon an SD epoch are briefly discussed.

IOP PUBLISHING LTD2019

Two-Tone Optomechanical Instability and Its Fundamental Implications for Backaction-Evading Measurements

Tobias Kippenberg, Liu Qiu, Itay Shomroni, Amir Youssefi

While quantum mechanics imposes a fundamental limit on the precision of interferometric measurementsof mechanical motion due to measurement backaction, the nonlinear nature of the coupling also leads toparametric instabilities that place practical limits on the sensitivity by limiting the power in theinterferometer. Such instabilities have been extensively studied in the context of gravitational wavedetectors, and their presence has recently been reported in Advanced LIGO. Here, we observeexperimentally and describe theoretically a new type of optomechanical instability that arises in two-tone backaction-evading (BAE) measurements, a protocol designed to overcome the standard quantumlimit. We demonstrate the effect in the optical domain with a photonic crystal nanobeam cavity and in themicrowave domain with a micromechanical oscillator coupled to a microwave resonator. In contrast to thewell-known parametric oscillatory instability that occurs in single-tone, blue-detuned pumping, and resultsfrom a two-mode squeezing interaction between the optical and mechanical modes, the parametricinstability in balanced two-tone optomechanics results from single-mode squeezing of the mechanical modein the presence of small detuning errors in the two pump frequencies. Counterintuitively, the instabilityoccurs even in the presence of perfectly balanced intracavity fields and can occur for both signs of detuningerrors. We find excellent quantitative agreement with our theoretical predictions. Since the constraints ontuning accuracy become stricter with increasing probe power, the instability imposes a fundamentallimitation on BAE measurements as well as other two-tone schemes, such as dissipative squeezing of opticaland microwave fields or of mechanical motion. In addition to identifying a new limitation in two-tone BAEmeasurements, the results also introduce a new type of nonlinear dynamics in cavity optomechanics.

2019

Two-Tone Optomechanical Instability and Its Fundamental Implications for Backaction-Evading Measurements

Tobias Kippenberg, Liu Qiu, Itay Shomroni, Amir Youssefi

2019