Quantum Physics: The Most Extreme 'Entanglement' Yet Between Photon Pairs

First Posted: Nov 09, 2015 12:24 PM EST

A new experiment has actually recorded some quantum weirdness. Scientists have reported the most extreme "entanglement" yet between pairs of photons.

"For some quantum technologies to work as we intend, we need to be confident that quantum physics is complete," said Poh Hou Shun, one of the researchers, in a news release. "Our new result increases that confidence."

Entanglement states that two particles, such as the photons in the experiment, can be married into a joint state. Once they are in this state, either particle observed on its own appears to behave randomly. Observed together, though, it can be seen that both particles are perfect synchronized.

In this latest study, the researchers performed a Bell test. Instead of closing loopholes, though, the researchers pushed entanglement towards its theoretical maximum.

The scientists created entangled photons by shining a laser through a crystal. The photons then interacted with the crystal in such a way that occasionally one split into two, and the pair emerged entangled. The team controlled the photons with an array of lenses, mirrors and other optical elements in order to maximize the effect.

In all, the researchers looked at 33.2 million optimized photon pairs. Each pair was split up and the photons measured separately. Then a correlation between the results was quantified.

In such a Bell test, the strength of the correlation says whether or not the photons were entangled. The measures involved are complex, but can be reduced to a simple number. Any value bigger than 2 is evidence for quantum effects at work. But there is also an upper limit.

"You need a very precise measurement to be able to distinguish the quantum limit, and that was our achievement," said Christian Kurtsiefer, one of the researchers.

The findings are published in the journal Physical Review Letters.