"Robust" entanglement to advance development of quantum imaging tech

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Researchers have been able to compensate for the disturbance entagled photons experience during propagation through a scattering layer and restore entanglement at the output

Researchers may have solved a key challenge of quantum entanglement that could help advance the development of new quantum-enhanced imaging and communications technologies.

Quantum entanglement is a fascinating property of quantum mechanics that allows two particles to maintain a close connection, regardless of the distance between them. 

Systems that harness entanglement underpin many potentially transformative breakthroughs in technology, including advanced microscopes and ultra-secure communications systems. 

However, entanglement is a fragile and difficult-to-detect property, which can make it challenging to use reliably in real-world conditions.

When pairs of entangled photons – the particles of light – propagate through cloudy or opaque materials such as biological tissues, or through swirling gases, entanglement can deteriorate and be rendered useless.

Now, however, in Physical Review X Quantum, scientists from the University of Glasgow, the Kastler Brossel lab and the Paris Institute of Nanosciences have described their ability to be able to keep particles entangled in previously impossible conditions.

The scientists share their development of an optical manipulation technique to preserve entanglement between photons travelling through challenging conditions. To demonstrate the technique, they built an experiment in which pairs of entangled photons were sent through a scattering layer. Usually, this causes the photons to be randomly scattered in all directions, and entanglement becomes undetectable.

Surprisingly, by acting on the particles before they enter the scattering layer, the researchers were able to compensate for the disturbance they experience during their propagation and restore entanglement at the output.

“Pre-mixing the photons before they pass through the scattering material allows us to restore entanglement at the other side,” said Dr Hugo Defienne, of the Paris Institute of Nanosciences and the University of Glasgow. “It’s a little bit like turning omelettes back into eggs, and it’s the first time that it’s been done in quantum technologies.”

The technique has the potential to make quantum entanglement much more robust in real-world environments by preserving entanglement in challenging situations. This could help advance new applications in quantum microscopy, where entangled photons could resolve higher-resolution images of tissue samples, or in communications, where messages could be more reliably encrypted and transmitted.

“The success of our research is a result of the combined expertise of a team with expertise in very distinct fields of optics,” said Defienne. “In Paris, Professor Sylvain Gigan’s experience in manipulating photons using lightwave shaping techniques was complemented by the quantum imaging methods and the single-photon cameras I developed in partnership with Professor Daniele Faccio at the University of Glasgow. 

“We’re looking forward to building on this work to develop further applications in the future.”  

In addition to receiving funding from the European Union’s Horizon 2020 research and innovation programme and the European Research Council, this work was supported by the UK’s Royal Academy of Engineering Chairs in Emerging Technologies Scheme, and the Engineering and Physical Sciences Research Council.

Image: Caleb Foster/shutterstock.com

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