News in Science

Scientists squeeze light past quantum limit

Tiny ripples The race to discover gravity waves may be getting closer to the finish line with scientists successfully squeezing light using quantum mechanics.

The detection of gravity waves is one of the Holy Grails of astronomy and astrophysics. It will allow researchers to study the inner workings of exploding stars and colliding black holes.

Einstein's general theory of relativity predicts these massive astronomical events generate tiny fluctuations, causing the fabric of space-time to expand and contract - like ripples on the surface of a pond.

These yet to be discovered waves require the most sensitive detectors ever built, but up until now they've not been sensitive enough.

Now an international team of scientists, which includes Professor David Blair, Director of the Australian International Gravity Wave Research Centre at the University of Western Australia, report on a new technique in the journal Nature Physics, which almost doubles the sensitivity of these detectors.

Blair says the GEO600 gravity wave observatory in Germany is the first practical application of this new technology, and is part of a global network called the Laser Interferometer Gravitational Wave Observatory (LIGO).

The observatory will measure tiny variations in the distance travelled by two halves of a laser beam that's been split along perpendicular arms of a kilometre-sized instrument called an interferometer.

But any the change in the beams caused by gravity waves is so tiny, it's drowned out by a quantum effect called vacuum fluctuations.

Empty space isn't really empty

These fluctuations, caused by the uncertainty principle of quantum mechanics involves virtual particles popping in and out of existence for short periods.

Scientists know it's real because they leave detectable traces. Virtual photons, for example, produce tiny shifts in energy levels in atoms and minute changes in the magnetic moment of electrons.

Blair says, "We overcome this by using so-called squeezed light, which changes quantum uncertainty in the frequencies monitored by the detectors".

"The key technology was pioneered by gravitational wave researchers at the Australian National University led by Professor David McClelland."

"Using special crystals, this squeezing process creates quantum entangled photons between the ferometer's mirrors, turning green light into infrared light, and turning one photon into two", says Blair.

Quantum entanglement happens when two interacting subatomic particles are separated, yet changes made to one will impact the other, even though they're not physically connected.

"The strange thing is, when you look at it, there's nothing there, yet this 'nothing' which is the vacuum fluctuation can be squeezed and we know it's real, because it changes the sensitivity of the detector," says Blair.

"It's mind blowing, changing the way we think about light and the universe".

"It will allow us to test theories such as time standing still on the surface of black holes and space getting warped to the most extreme degree possible".