2015 Theses Doctoral

The Classical and Quantum Aspects of the Detection of Gravitational Waves

Factourovich, Maxim

Detection of gravitational waves has been one of the major undertakings of science for the past several decades. The elusive phenomenon first emerged as a natural consequence of the A. Einstein's Theory of General Relativity, but for many years was beyond the reach of the existing technological capabilities. Today, a radical effort is underway to take the measurement technology to a new, unprecedented level of sensitivity, in order to give a definite answer to one of the most fundamental aspects of our understanding of the Universe.
The currently accepted detection scheme utilizes interference of near-infrared light inside a high-finesse Fabry-Perot cavity, and has achieved resolution on a scale of 10-21 as compared to the cavity length. At this scale, the signal becomes very sensitive to all kinds of unwanted inputs which include, but not limited to, the seismic activity, acoustic vibrations, thermal effects and radiation pressure noise. Moreover, the sensitivity requirements place it near the fundamental limit of quantum uncertainty which poses the ultimate barrier for lowering the detection threshold. Additionally, at the large kilometer-scale size of the installations, the signal propagation delays become significant enough to call for precise synchronization between the remote sensors and electronics within the main data collector. The need for this becomes even more evident considering a possibility of triangulation the otherwise non-directional signal, by unifying the data collected from different observatories spread around the globe.
In this work, we first address the aspect of precise timing synchronization implemented in the US-based Advanced Laser-Interferometer Gravitational-wave Observatories (LIGO) located at Hanford, WA and Livingston, LA. The developed Advanced LIGO Timing System allows for synchronization of virtually unlimited number of devices to an accuracy of better than 1 microsecond, regardless of the distances involved. The machinery uses Field Programmable Gate Array (FPGA) logic at its core processing units. The FPGA chips are driven by oscillators synchronized to both, a Master atomic clock and the Global Positioning System (GPS) satellites for a precise calibration with redundancy. The timings signals are encoded in a pulse-modulated signal and distributed over the network via optical fibers.
Additionally, we present a prototype device that allows overcoming the quantum sensitivity barrier without violating the Uncertainty Principle, also known as the Squeezer. We demonstrate the laser shotnoise reduction of up to 9 dB in a test setup, that eventually translated to a 25% increase in the detector sensitivity, upon injection of the squeezed light into the operational LIGO
interferometer.