Gravitational Radiation

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New designs will be invented for advanced gravitational-wave detectors to operate in LIGO (the Laser Interferometer Gravitational-Wave Observatory) in the 2008--2010 time frame; and the performance of these new detectors will be predicted by theoretical analyses. The principal goal of these new detectors will be to circumvent a new type of noise that will arise when the detectors are improved to the level expected in 2008-2010; noise due to the quantum mechanical behavior of the mirrors in LIGO, which move in response to passing gravitational waves. These new detectors are called "Quantum-Nondemolition" (QND) gravitational-wave detectors because they will enable the gravitational-wave signal to evade being demolished by the quantum mechanical behavior of the mirrors. Additional theoretical studies will focus on other types of noise that these QND detectors (and other advanced detectors in LIGO) must face, and on how to control these noises. These other noises include fluctuating gravitational forces from turbulence in the earth's atmosphere and from weak seismic waves in the ground beneath the detectors, and noise from thermal vibrations of atoms in LIGO's mirrors. Finally, theoretical studies of various sources of gravitational waves will be carried out, with the goal of providing guidance for the design of LIGO's data analysis software, and guidance for the planning of LIGO's gravitational-wave searches and observations.This research will lay foundations for long-term improvements of LIGO's scientific and technical capabilities. It will thereby help to expand greatly the volume of the universe through which LIGO can search for colliding black holes and other sources of gravitational waves. The QND research also has broader implications: It is a forefront portion of the new field of "quantum metrology"---a twenty-first century technology that will make use of, manipulate, and control the quantum mechanical behavior of macroscopic objects, and will manipulate quantum mechanical information.