Optimal Quantum Measurements in Gravitational Radiation Detectors

Vladimir B. Braginsky, Yu.I. Vorontsov, F. Ya. Khalili

Farid Ya Khalili

Farit Ya. Khalili

Vladimir B. Braginskii, Yu.I. Vorontsov, F. Ya. Khalili

When continuous measurement is made with an instrument whose interaction with the gravitational antenna has a Hamiltonian proportional to the instantaneous coordinate, the sensitivity of the detector has in principle a limit. It becomes necessary to use a procedure with a pulsed measurement of the coordinate.

Hudson A. Loughlin, Germain Tobar, Evan D Hall +1 more

In a consistent description of the quantum measurement process, whether the wave or particlelike aspect of a system is revealed depends on the details of the measurement chain, and cannot be interpreted as an objective fact about the system independent of the measurement. We show precisely how this comes to be in the measurement of gravitational radiation. Whether a wave or particlelike aspect is revealed is a property of the detector employed at the end of the quantum measurement chain, rather than of the meter, such as a gravitational-wave (GW) antenna or resonant bar, used to couple the radiation to the detector. A linear detector yields no signal for radiation in a Fock state and a signal proportional to the amplitude in a coherent state—supporting a wavelike interpretation. In contrast, the signal from a detector coupled to the meter's energy is nonzero only when the incident radiation contains at least a single graviton. Thus, conceptually simple modifications of contemporary GW antennae can reveal wave-particle duality in the measurement of gravitational radiation.

S. L. Danilishin, Farid Ya. Khalili

The fast progress in improving the sensitivity of the gravitational-wave detectors, we all have witnessed in the recent years, has propelled the scientific community to the point at which quantum behavior of such immense measurement devices as kilometer-long interferometers starts to matter. The time when their sensitivity will be mainly limited by the quantum noise of light is around the corner, and finding ways to reduce it will become a necessity. Therefore, the primary goal we pursued in this review was to familiarize a broad spectrum of readers with the theory of quantum measurements in the very form it finds application in the area of gravitational-wave detection. We focus on how quantum noise arises in gravitational-wave interferometers and what limitations it imposes on the achievable sensitivity. We start from the very basic concepts and gradually advance to the general linear quantum measurement theory and its application to the calculation of quantum noise in the contemporary and planned interferometric detectors of gravitational radiation of the first and second generation. Special attention is paid to the concept of the Standard Quantum Limit and the methods of its surmounting.