Scientists unveil the very first picture of quantum entanglement

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Full mode images recording the violation of a Bell inequality in four images. (A) The four coincidence count images are presented, which correspond to the images of the phase circle acquired with the four phase filters with different orientations, θ2 = {0 °, 45 °, 90 °, 135 °}, necessary to the realization of the bell test. Scale bars, 1 mm (in the plane of the object). (B to E) Counts of coincidence counts as a function of the orientation angle 01 of the phase step along the object are presented. As indicated, these results are obtained by unfolding the ROIs represented by red rings and are extracted from the images presented in (A). The blue dots in the graphs represent the angular region coincidence counts in the ROIs, and the red curves represent the best adjustments of the experimental data by a cosine squared function. (B) to (E) correspond to phase filter orientations θ2 of 0 °, 45 °, 90 ° and 135 °, respectively. Credit: Progress of science (2019). DOI: 10.1126 / sciadv.aaw2563

For the first time, physicists have managed to photograph a powerful form of quantum entanglement called Bell entanglement, capturing the visual evidence of an elusive phenomenon that an Albert Einstein, disconcerted, once had called "spooky action at a distance".

Two particles that interact with each other – for example two photons crossing a beam splitter – can sometimes remain connected and instantly share their physical states, regardless of the distance between them. This connection is known as quantum entanglement and it underlies the field of quantum mechanics.

Einstein thought that quantum mechanics was "phantasmagorical" because of the immediacy of the apparent interplay between two entangled particles, which seemed inconsistent with elements of his special theory of relativity.

Later, Sir John Bell formalized this concept of nonlocal interaction describing a strong form of entanglement exhibiting this phantasmagoria. Today, while Bell 's entanglement is being exploited in practical applications such as quantum computing and cryptography, it has never been captured in a single image.

In an article published today in the journal Progress of science, a team of physicists from the University of Glasgow describe how they made Einstein's phantasmagoria visible on an image.

They have developed a system that triggers a tangled photon flow from a quantum light source onto "unconventional objects" – displayed on liquid crystal materials that alter the photon phase as they pass through. .

They set up a super sensitive camera capable of detecting single photons that would only take an image if it sighted both a photon and its entangled "twin", thus creating a visible record of entanglement of photons.

Imaging configuration to perform a test of inequality of Bell in images. A BBO crystal pumped by an ultraviolet laser is used as a source of entangled photon pairs. The two photons are separated on a beam splitter (BS). An intensified camera triggered by a SPAD makes it possible to acquire ghost images of a phase object placed on the path of the first photon and filtered not locally by four different spatial filters that can be displayed on an SLM (SLM 2) placed in the other arm. When triggered by SPAD, the camera acquires coincidence images that can be used to perform a Bell test. Credit: Progress of science (2019). DOI: 10.1126 / sciadv.aaw2563

Dr. Paul-Antoine Moreau, of the faculty of physics and astronomy at the University of Glasgow, is the principal author. Dr. Moreau said: "The image we managed to capture is an elegant demonstration of a fundamental property of nature, seen for the very first time in the form of an image.

"It's an exciting result that could be used to advance the emerging field of quantum computing and lead to new types of imaging."

The document, titled "Non-local Bell-like Imaging Behavior," is published in Progress of science.