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Squeezed light helps measure gravitational waves

Photonics Spectra
Nov 2011
Ashley N. Paddock, ashley.paddock@photonics.com

HANNOVER, Germany – A new “squeezed light” method improves the sensitivity and accuracy of the interferometers used to measure gravitational waves.

Observing the gravitational waves that result from supernova explosions and other cosmic events requires extremely sensitive metrology techniques. A gravitational wave’s signal is so small that it is usually dwarfed by the noise generated by the quantum mechanical fluctuations of the light beams, and this shot noise limits the accuracy of the interferometer.


A highly complex laser system produces light in the gravitational wave detector GEO600 that is particularly quiet. Courtesy of Max Planck Institute for Gravitational Physics.


A new “squeezing” process developed at Max Planck Society and Leibniz University Hannover minimizes this uncertainty to produce laser light with almost no fluctuations, thus improving the measuring accuracy and increasing the sensitivity of gravitational wave detectors such as the GEO600 at the university’s Center for Quantum Engineering and Space-Time Research.

The squeezed light method generates a completely new quality of laser light, which the team used to increase the measurement sensitivity of the GEO600 to 150 percent. This is an important step toward direct sensing of gravitational waves, the researchers say.


3-D visualization of gravitational waves produced by two orbiting black holes. Courtesy of Henze, NASA.


The scientists fed the squeezed light, in addition to the normal laser light, into the interferometer. If the two light fields superimpose, the laser beam that results has more uniform intensity than the original signal beam. Thus, they determined that their method smooths out irregularities caused by quantum physical effects in the signal of the detector.

The results appeared online Sept. 11 in Nature Physics (doi: 10.1038/nphys2083). Since April of last year, the squeezed laser light has undergone a longer test phase at GEO600 and is currently being used in the search for gravitational waves.


GLOSSARY
detector
1. A device designed to convert the energy of incident radiation into another form for the determination of the presence of the radiation. The device may function by electrical, photographic or visual means. 2. A device that provides an electric output that is a useful measure of the radiation that is incident on the device.
gravitational waves
Postulated by Einstein in his theory of relativity. They are waves traveling at the speed of light and exerting force on matter in their path. They are produced by changes in the distribution of matter.
interferometer
An instrument that employs the interference of lightwaves to measure the accuracy of optical surfaces; it can measure a length in terms of the length of a wave of light by using interference phenomena based on the wave characteristics of light. Interferometers are used extensively for testing optical elements during manufacture. Typical designs include the Michelson, Twyman-Green and Fizeau interferometers. The basic interferometer components are a light source, a beamsplitter, a reference...
metrology
The science of measurement, particularly of lengths and angles.
shot noise
Noise generated by the random variations in the number and velocity of the electrons from an emitter.
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