Resonant Dampers for Parametric Instabilities in Gravitational Wave Detectors

Advanced gravitational wave interferometric detectors will operate at their design sensitivity with nearly 1MW of laser power stored in the arm cavities. Such large power may lead to the uncontrolled growth of acoustic modes in the test masses due to the transfer of optical energy to the mechanical modes of the arm cavity mirrors. These parametric instabilities have the potential of significantly compromising the detector performance and control. Here we present the design of "acoustic mode dampers" that use the piezoelectric effect to reduce the coupling of optical to mechanical energy. Experimental measurements carried on an Advanced LIGO-like test mass shown a 10-fold reduction in the amplitude of several mechanical modes, thus suggesting that this technique can greatly mitigate the impact of parametric instabilities in advanced detectors

The control of the Virgo interferometer for gravitational wave detection

VIRGO is a recycled Michelson interferometer where each arm is replaced by a 3 km long Fabry-Perot cavity. It is designed to detect gravitational waves emitted by astrophysical sources. Mirrors are suspended in vacuum by high performance suspensions, so that detection is possibly starting from very low frequencies, a few Hz, up to a few kHz. The work presented in this thesis is focused on the longitudinal control of VIRGO, that is the control of the position of the test masses along the light beam direction. Relative displacements of the mirrors need to be actively controlled in order to bring and keep the interferometer on its working point. By following the evolution of the VIRGO commissioning, suitable strategies have been designed and applied to differ- ent optical confgurations: a single Fabry-Perot cavity, a Michelson interferometer with Fabry-Perot cavities in the arms (the recombined ITF), and finally the full interferometer (the recycled ITF). Once the lock of full VIRGO was achieved, the process of investigating and reducing the longitudinal control noises coupled into the dark fringe signal began

Machine Learning for Quantum-Enhanced Gravitational-Wave Observatories

Machine learning has become an effective tool for processing the extensive data sets produced by large physics experiments. Gravitational-wave detectors are now listening to the universe with quantum-enhanced sensitivity, accomplished with the injection of squeezed vacuum states. Squeezed state preparation and injection is operationally complicated, as well as highly sensitive to environmental fluctuations and variations in the interferometer state. Achieving and maintaining optimal squeezing levels is a challenging problem and will require development of new techniques to reach the lofty targets set by design goals for future observing runs and next-generation detectors. We use machine learning techniques to predict the squeezing level during the third observing run of the Laser Interferometer Gravitational-Wave Observatory (LIGO) based on auxiliary data streams, and offer interpretations of our models to identify and quantify salient sources of squeezing degradation. The development of these techniques lays the groundwork for future efforts to optimize squeezed state injection in gravitational-wave detectors, with the goal of enabling closed-loop control of the squeezer subsystem by an agent based on machine learning

Decoherence and degradation of squeezed states in quantum filter cavities

Squeezed states of light have been successfully employed in interferometric gravitational-wave detectors to reduce quantum noise, thus becoming one of the most promising options for extending the astrophysical reach of the generation of detectors currently under construction worldwide. In these advanced instruments, quantum noise will limit sensitivity over the entire detection band. Therefore, to obtain the greatest benefit from squeezing, the injected squeezed state must be filtered using a long-storage-time optical resonator, or “filter cavity,” so as to realize a frequency-dependent rotation of the squeezed quadrature. While the ultimate performance of a filter cavity is determined by its storage time, several practical decoherence and degradation mechanisms limit the experimentally achievable quantum noise reduction. In this paper we develop an analytical model to explore these mechanisms in detail. As an example, we apply our results to the 16 m filter cavity design currently under consideration for the Advanced LIGO interferometers.National Science Foundation (U.S.) (Laser Interferometer Gravitational Wave Observatory Cooperative Agreement PHY-0757058

Prospects for doubling the range of Advanced LIGO

In the coming years, the gravitational wave community will be optimizing detector performance for a variety of astrophysical sources that make competing demands on the detector sensitivity in different frequency bands. In this paper we describe a number of technologies that are being developed as anticipated upgrades to the Advanced LIGO detector, and quantify the potential sensitivity improvement they offer. Specifically, we consider squeezed light injection for reduction of quantum noise, detector design and materials changes which reduce thermal noise, and mirrors with significantly increased mass. We explore how each of these technologies impacts the detection of the most promising gravitational wave sources, and suggest an effective progression of upgrades which culminate in a factor of two broadband sensitivity improvement

A Gravitational Wave Detector with Cosmological Reach

Twenty years ago, construction began on the Laser Interferometer Gravitational-wave Observatory (LIGO). Advanced LIGO, with a factor of ten better design sensitivity than Initial LIGO, will begin taking data this year, and should soon make detections a monthly occurrence. While Advanced LIGO promises to make first detections of gravitational waves from the nearby universe, an additional factor of ten increase in sensitivity would put exciting science targets within reach by providing observations of binary black hole inspirals throughout most of the history of star formation, and high signal to noise observations of nearby events. Design studies for future detectors to date rely on significant technological advances that are futuristic and risky. In this paper we propose a different direction. We resurrect the idea of a using longer arm lengths coupled with largely proven technologies. Since the major noise sources that limit gravitational wave detectors do not scale trivially with the length of the detector, we study their impact and find that 40~km arm lengths are nearly optimal, and can incorporate currently available technologies to detect gravitational wave sources at cosmological distances $(z \gtrsim 7)$