Gravitational waves were predicted by Einstein but have long remained undetected. To look for them, scientists use devices called laser interferometers, which measure the time it takes a split beam of laser light to travel between suspended mirrors. The waves are expected to distort the laser's travel time - but so far scientists can't measure this accurately enough.
The accuracy of these devices is limited by a quantum phenomenon of light called 'shot noise' - a type of electronic interference.
Using a new quality of laser light, which radiates much more calmly than a conventional laser, researchers reported yesterday in Nature Physics that they have curbed this interference and improved measuring accuracy in their detectors by roughly 50%.
"Squeezed light is a completely new approach," said physicist and lead author Roman Schnabel, from the Max Planck Institute for Gravitational Physics in Germany.
"One can say that for the first time a `technology' is based on one of the distinct features of quantum physics itself. We were able to leave the stage of laboratory experiments and realize a real application."
Travel time weakens waves
The findings are an an exciting step forward for the Laser Interferometry Gravitational-Wave Observatory (LIGO) project in its quest to observe gravitational waves using Earth-based detectors.
Albert Einstein first predicted the existence of gravitational waves in 1916 in his theory of general relativity. The presence of large amounts of mass or energy can distort the space-time fabric causing it to curve, and when they move suddenly, this curvature ripples outward - like the ripples in a pond after a fish jumps.
Violent astronomical events such as black hole collisions and supernovae can cause gravitational waves. In the immediate vicinity of these objects, gravitational waves would be immensely strong, said Schnabel.
However, after travelling billions of light years to reach the Earth they are significantly weakened, making them incredibly difficult to detect. So far they have eluded scientists.
Theoretical predictions based on Einstein's theory indicate current detectors must be improved by another factor of about three to 10 to reach a high probability of successful detection, said Schnabel.
"Squeezed light is a new technology, which has now proven to significantly contribute to realising this last factor," Schnabel said. "[And] the improvement factor of 1.5 is just the beginning. A factor of three due to squeezed light is possible with today's technology."
Lasers superimposed
In a laser interferometer, a laser is split into two beams and shot down long, perpendicular vacuum tubes before reflecting off mirrors back to where they started.
If the distance measured by the light is exactly the same, all the light will be directed back to the original source, but if there is any difference in the distance, some light will be redirected to a photodetector for further analysis.
The idea is that space-time ripples caused by gravitational waves will cause the distance measured by the light beam to change, and the amount of light falling on the photodector to vary.
"We now feed the squeezed light into the interferometer, in addition to our normal laser light," explained Schnabel. "If the two light fields then superimpose, the resulting laser beam has a much more uniform intensity, compared to the original signal beam.
"We thus smooth out the irregularities caused by quantum physical effects in the detector signal," he added.
New view on the universe
"This is the first time this technology has been used outside of a test laboratory anywhere in the world," said David McClelland, a physicist at the Australian National University in Canberra and a key investigator for LIGO-Australia.
"The detection of gravitational waves would open a new window for astronomy and create a completely new way of sensing the Universe, akin to being able to hear for the very first time," he added.
The LIGO collaboration is in the process of testing a squeezed light source built at the ANU on the 4 km long LIGO interferometer in Washington State in the U.S. According to Schnabel, testing on this observatory and Europe's envisaged 10km Einstein Telescope, could further improve detection capabilities.
source:Cosmos Online
Gathered by: Sh.Barzanjeh(shabirbarzanjeh@gmail.com)
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