First photo of a quantum entanglement

Researchers make quantum-mechanical coupling of photons visible

These slightly blurry pictures are the first direct pictures of a quantum physical entanglement. © Moreau et al. / Science Advances, doi: 10.1126 / sciadv.aaw2563
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Einstein's "ghostly long-distance effect" in the picture: For the first time, physicists have succeeded in capturing the quantum-physical phenomenon of entanglement in the photograph. Her apparatus only showed a picture of the photons when she registered both copies of the linked "twins". This technique makes the entanglement directly visible for the first time and opens up new possibilities of application in quantum physics, the researchers report in the journal "Science Advances".

In the case of quantum physical entanglement, the states of two particles are coupled together in such a way that the change of state of one automatically causes that of the partner. This happens instantaneously and independently of the distance. Albert Einstein called this phenomenon therefore also as "ghostly remote effect". The entanglement forms the basis for quantum communication, for quantum computers and many other applications of quantum physics.

Experiment setup for the photo recording of the quantum entanglement. BS = beam splitter, SLM = spatial light modulator, SPAD = single-photon avalanche diode © Moreau et al. / Science Advances, doi: 10.1126 / sciadv.aaw2563

Picture only with entanglement

Capturing this phenomenon for the first time has now been achieved by Paul-Antoine Moreau and his team from the University of Glasgow. Until now, entanglement could only be demonstrated by measurement: If non-local correlations occur, for example, in the state of photons, this is considered a violation of the so-called Bell's inequality and thus an indication of their entanglement.

For their experiment, the researchers first generated a stream of entangled photon pairs, which they steered with a beam splitter on two different tracks. Both photons were passed through a liquid crystal, which changes their phase. At the end of an arm stood a special camera, which only produced a picture of the arriving photon when a detector on the other arm registered the restricted partner of this photon.

Blurred "crescent moon"

The first photos of the "ghostly long-distance effect" are similar to two blurred crescent spikes standing opposite each other. However, they represent the twisted phases of the confined photons and are the first image of the violation of Bell's inequality typical of quantum confinement. "Our demonstration proves that one can capture the signature of this behavior in a single image, " say the researchers. display

"Obtaining images of such a fundamental quantum effect demonstrates that images themselves can capture the essence of the quantum world, " explains Moreau. "This is an exciting result that could lead to new types of imaging and could advance the field of quantum computing." (Science Advances, 2019; doi: 10.1126 / sciadv.aaw2563)

Source: University of Glasgow

- Nadja Podbregar