Physicists reveal the very first image of quantum entanglement between two particles

Among the many phenomena arising from quantum mechanics, quantum entanglement is certainly one of the strangest. When two particles are entangled, they cease to be objects in their own right to become one and the same physical system of solidarity; any modification of one has instantaneous repercussions on the other, regardless of the distance that separates them. For the first time, researchers from the University of Glasgow provided the very first image of a pair of entangled photons, thus demonstrating the violation of Bell's inequalities.

This particular photo shows the entanglement between two photons - the boson of the electromagnetic interaction. Paul-Antoine Moreau, lead author of the study, states that the image is " an elegant demonstration of a fundamental property of nature ". The study was published in the journal Science Advances.

To capture this phenomenon, Moreau and a team of physicists have created a system that sends entangled photon fluxes on what they have described as "unconventional objects." The experiment consisted of capturing four photon images under four different phase transitions.

The researchers succeeded in imaging the entanglement of photon pairs crossing series of four-phase transitions. Credits: Paul-Antoine Moreau et al. 2019

It is actually a composite image of several images of photons that pass through a series of four-phase transitions. Basically, physicists have divided the entangled photons and sent a beam through a liquid crystal material known as barium β-borate, triggering four-phase transitions. At the same time, they captured photos of the entangled pair passing through the same phase transitions, even though it had not crossed the liquid crystal.

Scheme of experimental protocol used by researchers. The entangled photon beam is from the bottom left, half of the entangled pair splits to the left and passes through the four phase filters. The others that go straight have not gone through the filters, but have undergone the same phase changes. Credits: Paul-Antoine Moreau et al. 2019

The violation of Bell's inequalities in images

The camera was able to capture the images of these different sequences of events at the same time, showing that the two photons had changed in the same way despite their spatial remoteness.

Physicists first obtain a raw image from the four-phase filter (left). Then, thanks to a special treatment (de-scanning), they get a clearer picture of the entanglement, which confirms the violation of Bell's inequalities. Credits: Paul-Antoine Moreau et al. 2019

The physicist John Stewart Bell has defined a series of conditions called "Bell inequalities". The latter characterize relations that must be respected by measurements on entangled states, in the context of a local deterministic theory with hidden variables. Demonstrating the entanglement between two particles amounts to violating these inequalities.

" We report here an experiment demonstrating the violation of a Bell inequality in the observed images. This result paves the way for new quantum imaging schemes ... and suggests promising perspectives for quantum information schemes based on spatial variables "concludes the team.


Imaging Bell-type nonlocal behavior
Paul-Antoine Moreau*, Ermes Toninelli, Thomas Gregory, Reuben S. Aspden, Peter A. Morris and Miles J. Padgett*
Science Advances 12 Jul 2019:
Vol. 5, no. 7, eaaw2563
DOI: 10.1126/sciadv.aaw2563

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