Sensitivity Of Gravitational Wave Detectors Research Articles

Quantum limitations on the sensitivity of gravitational wave detectors with free masses

The problem of recording a classical disturbance by tracking the coordinate of a free particle is examined within the scope of nonrelativistic quantum mechanics. The absence of the fundamental limitation on the sensitivity — the “standard quantum limit” — is proven. An arbitrarily small disturbance can be recorded with preparation of the system in a quantum state having a negative quantum correlation coefficient between the observable coordinate and momentum. It is shown that it belongs to the collective coherent states — the condensed states. Arguments are presented for the absence of fundamental quantum limits on the magnitude of the recordable disturbance in the measurement of an arbitrary observable with a continuous spectrum.

Gravitational wave astronomy — Potential and possible realisation

Since the pioneering work of Joseph Weber more than a decade ago there has been a continuing effort towards the development of more sensitive gravitational wave detectors. There are a number of interesting astrophysical sources of gravitational waves including coalescing compact binary star systems, stellar collapses and rotating neutron stars, and to detect all of these is likely to require a strain sensitivity better than 10 −22 over a bandwidth of a few hundred Hz at frequencies at or below 1kHz. To achieve such sensitivity requires considerable experimental ingenuity; however work in a number of laboratories suggests that such performance should be attainable using laser interferometry between freely suspended masses separated by a distance of the order of a kilometre. This paper includes a review of possible sources and outlines methods of detection currently being developed or planned, with particular emphasis on long baseline laser interferometers.

Back-action-evading measurement of optical fields with the use of a four-wave mixer

Recent investigations on the ultimate sensitivity of gravitational-wave detectors have led to a new measurement strategy known as "back-action evasion" which allows one to measure precisely one component of an oscillator's motion without disturbing that component. This detection strategy can be carried out on electromagnetic field modes as well. Here a scheme, using a degenerate four-wave mixer, is presented for carrying out back-action-evading measurements on optical field modes.

Local relative motion in general relativity

The distinction is drawn between problems in which single particle motion has physical significance and those in which relative motion between pairs of particles must be considered. Local relative motion is considered from the standpoint of the equation of geodesic deviation, expressed in arbitrary coordinates and in geodesic Fermi coordinates. A simple alternative approach to geodesic deviation using synchronous reference frames is described. Examples of relative motion in the Schwarzschild field and in a gravitational wave are discussed. Criticism of the efficacy of cryogenic cooling to enhance gravitational wave detector sensitivity is shown to be invalid. However, a cautionary note is expressed with regard to the necessity of a local observer to detect deviations from local planeness.