Simulation of opto-mechanical systems in the presence of ponderomotive squeezing effects

Context and motivations The interplay between optical and mechanical modes in a system produces a wealth of interesting effects which have been investigated and exploited in many different areas. In the context of interferometric gravitational waves detectors the opto-mechanical coupling which originates between mirrors and laser by means of radiation pressure has been proposed to be used, for example, to reduce the thermal noise of the mirrors by cooling their motion. We are particularly interested in its application to reduce the fundamental noise which stems from the quantum nature of light and which will eventually limit the sensitivity of new generation detectors. In this noise, known as “quantum noise”, two different contributions can be individuated: the first one is shot noise, caused by the fluctuations of the number of photons in laser beams, which is higher when the laser power is low; the second one is radiation pressure noise, caused by quantum fluctuations of the laser amplitude, whose effect increases for higher values of the power and usually is more relevant at lower frequencies. It has been proposed to circumvent the lower bound set by quantum noise, usually referred to as standard quantum limit (SQL), by using light with particular noise features. In an ordinary laser, described by a coherent state, the amplitude quadrature uncertainty equals the phase quadrature uncertainty and their product is the minimum possible allowed by the Heisenberg's uncertainty principle. However, quantum physics does not prevent us from modifying quantum fluctuation and new quantum states can be obtained, so that phase and amplitude quadrature uncertainty are no longer equal. For these states, referred to as “squeezed”, the phase uncertainty can be reduced at the expense of amplitude uncertainty which is bound to increase in order to make the uncertainty principle hold true. If the information we need to measure is kept in the phase of the field (as it happens for the mirrors displacement in gravitational waves detectors), we can have an intuitive idea of how, for these states, noise can go below SQL. Shot noise and radiation-pressure noise together need not to adhere to the SQL if they are correlated: in effect squeezed light is generated by inducing correlations between amplitude and phase fluctuations. So far the most effective techniques for producing squeezed light make use of non-linear means to create this correlation. However, in theory, the mere interaction of the laser light with a movable mirror is enough: indeed an amplitude fluctuation of the input field generates a displacement of the suspended mirror which in turn will affect the phase fluctuations. This effect is referred to as ponderomotive squeezing and it is particularly interesting as it naturally arises in interferometric detectors, but due to the intrinsic weakness of radiation pressure fluctuation with respect to other noise sources, it is extremely difficult to observe. Goals and structure of the thesis This thesis focuses on the generation of ponderomotive squeezing and arises within the collaboration “Progetto PRIN di Ponderomotive Squeezing” (see www.ppps.it) which aims to build a dedicated interferometer to observe directly this squeezing effect. The main goal of this work is the development of a code able to simulate opto-mechanical effects in optical systems. In order to improve the accuracy of the simulation, optical fields are not regarded as plane waves but are decomposed in Hermite-Gauss (HG) modes. This allows to take into account tilting effects on the mirrors due to a non-zero torque of the radiation pressure. For each HG mode, the field is split in a classical part and in a fluctuating part. The first is evaluated using a classical model and it defines the equilibrium point for the mirrors, around which the dynamics is linearized. In order to describe the quantum fluctuations around a classical carrier we used the two photon formalism, where such fluctuations are treated as amplitude and phase fluctuations for sidebands of the carrier. It provides an effective way to describe the correlations introduced by the interaction of the field with optical elements like movable mirrors. We generalized this formalism, which was developed for plane waves, to the case of HG modes. In the first part of the work we describe classical opto-mecanical effects in a Fabry-Perot cavity with movable mirrors where the circulating light is decomposed in HG modes. Afterward the light fields are quantized and also the opto-mechanical effects are presented from a quantum point of view. In the second part we illustrate the operating principles of the simulation and present some results for the squeezing which is possible to obtain both in the case of a large interferometric gravitational wave detector and in a smaller dedicated cavity such as the one proposed in. We also included the possibility of simulating thermal noise in the system in order to compare its modulation effect on mirrors with those of quantum fluctuations. Lastly we briefly discuss the possibility of a further development of the simulation in order to take into account effects which appears beyond the linear approximation used

Estimation of losses in a 300 m filter cavity and quantum noise reduction in the KAGRA gravitational-wave detector

International audienceThe sensitivity of the gravitational-wave detector KAGRA, presently under construction, will be limited by quantum noise in a large fraction of its spectrum. The most promising technique to increase the detector sensitivity is the injection of squeezed states of light, where the squeezing angle is dynamically rotated by a Fabry-Pérot filter cavity. One of the main issues in the filter cavity design and realization is the optical losses due to the mirror surface imperfections. In this work we present a study of the specifications for the mirrors to be used in a 300 m filter cavity for the KAGRA detector. A prototype of the cavity will be constructed at the National Astronomical Observatory of Japan, inside the infrastructure of the former TAMA interferometer. We also discuss the potential improvement of the KAGRA sensitivity, based on a model of various realistic sources of losses and their influence on the squeezing amplitude

First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data

Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signalto- noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11 pulsars using data from Advanced LIGO’s first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far

Swift-BAT GUANO follow-up of gravitational-wave triggers in the Third LIGO–Virgo–KAGRA Observing Run

We present results from a search for X-ray/gamma-ray counterparts of gravitational-wave (GW) candidates from the third observing run (O3) of the LIGO–Virgo–KAGRA network using the Swift Burst Alert Telescope (Swift-BAT). The search includes 636 GW candidates received with low latency, 86 of which have been confirmed by the offline analysis and included in the third cumulative Gravitational-Wave Transient Catalogs (GWTC-3). Targeted searches were carried out on the entire GW sample using the maximum-likelihood Non-imaging Transient Reconstruction and Temporal Search pipeline on the BAT data made available via the GUANO infrastructure. We do not detect any significant electromagnetic emission that is temporally and spatially coincident with any of the GW candidates. We report flux upper limits in the 15–350 keV band as a function of sky position for all the catalog candidates. For GW candidates where the Swift-BAT false alarm rate is less than 10−3 Hz, we compute the GW–BAT joint false alarm rate. Finally, the derived Swift-BAT upper limits are used to infer constraints on the putative electromagnetic emission associated with binary black hole mergers

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Swift-BAT GUANO follow-up of gravitational-wave triggers in the third LIGO-Virgo-KAGRA observing run

We present results from a search for X-ray/gamma-ray counterparts of gravitational-wave (GW) candidates from the third observing run (O3) of the LIGO-Virgo-KAGRA (LVK) network using the Swift Burst Alert Telescope (Swift-BAT). The search includes 636 GW candidates received in low latency, 86 of which have been confirmed by the offline analysis and included in the third cumulative Gravitational-Wave Transient Catalogs (GWTC-3). Targeted searches were carried out on the entire GW sample using the maximum--likelihood NITRATES pipeline on the BAT data made available via the GUANO infrastructure. We do not detect any significant electromagnetic emission that is temporally and spatially coincident with any of the GW candidates. We report flux upper limits in the 15-350 keV band as a function of sky position for all the catalog candidates. For GW candidates where the Swift-BAT false alarm rate is less than 10$^{-3}$ Hz, we compute the GW--BAT joint false alarm rate. Finally, the derived Swift-BAT upper limits are used to infer constraints on the putative electromagnetic emission associated with binary black hole mergers.Comment: 50 pages, 10 figures, 4 table

Études optiques et de bruit pour Advanced Virgo et cavités de filtrage pour la réduction du bruit quantique dans les détecteurs interférométriques d' ondes gravitationnelles

Gravitational-wave astronomy has started in September 2015 with the first detection of a binary black-hole merger by LIGO. Since then, several black-hole mergers and a binary neutron star merger have been observed. Advanced Virgo joined the two LIGO detector in the observation run, in August 2017, highly increasing the local- ization capabilities of the network. In order to fully exploit the scientific potential of this new-born field, a huge experimental effort is needed to bring the instruments at their design sensitivity and to further improve them. This thesis, developed in this context, it is composed of two parts. The first is about Advanced Virgo : we have developed an automatic noise budget for the laser frequency noise and we have performed optical characterization measurements for the kilometric arm cavi- ties. Round trip losses as low as 80 ppm have been measured. They are among the lowest ever measured for beams of these size. The second part is about the design and development of a 300 m filter cavity, a prototype to demonstrate the frequency dependent squeezing production with properties needed for a broadband quantum noise reduction in the future upgrades of KAGRA, Advanced Virgo and Advanced LIGO. We have contributed to the design and integration phases of the project. We have first made the optical design of the cavity, including the the specifications for the main cavity optics and a detailed estimation of the squeezing degradation sources . We have then developed a local control system for the mirrors, assembled the sus- pensions, and finally aligned and brought the cavity in resonance with the laser light.L’astronomie gravitationnelle a débuté en septembre 2015 avec la première détection de la fusion de deux trous noirs par LIGO. Depuis lors, plusieurs fusions de trous noirs et une fusion d’étoiles à neutrons ont été observées. Advanced Virgo a rejoint les deux observatoires LIGO dans la prise de données en août 2017, augmentant fortement les capacités de localisation du réseau. Afin d’exploiter pleinement le potentiel sci- entifique de ce nouveau domaine, un énorme effort expérimental est nécessaire pour améliorer la sensibilité des interféromètres. Cette thèse, développée dans ce contexte, est composée de deux parties. La première concerne Advanced Virgo: nous avons développé un budget de bruit automatique pour le bruit de fréquence du laser et nous avons effectué des mesures de caractérisation optique pour les cavités de bras kilométriques. Des pertes aller-retour aussi faibles que 80 ppm ont été mesurées. Elle sont parmi les plus basse jamais mesurées avec un faisceau de cette taille. La deux- ième partie concerne la conception et le développement d’une cavité de filtrage de 300 m, un prototype pour démontrer la production de lumière squeezing dépendante de la fréquence avec les propriétés nécessaires pour une réduction du bruit quan- tique à large bande dans KAGRA, Advanced Virgo et Advanced LIGO. Nous avons contribué à la fois aux phases de conception et d’intégration du projet. Nous avons d’abord fait le design optique de la cavité, y compris les spécifications pour l’optique de la cavité et une estimation détaillée des sources de dégradation pour le squeez- ing. Nous avons donc développé un système de contrôle pour les miroirs, assemblé les suspensions et finalement aligné et mis la cavité en résonance avec la lumière laser