A team of physicists was able for the first time to encode a hologram using entangled photons. According to a new study published in the journal Nature Physics, a team of physicists from the University of Glasgow, Scotland, has for the first time managed to overcome the limitations of conventional holography. They have successfully encoded the information of a hologram, thanks to a technique based on quantum entanglement, and more precisely on entangled photons.
This innovative method could lead to a decisive improvement in the use of holography in various fields. Such as in medical imaging and quantum communication, and therefore also for future quantum computers.
The conventional Holography
It is a technique that is used to create a two-dimensional representation of a three-dimensional object with a laser light beam divided into two paths. The first ray, or object ray, is sent towards the object to be reproduced and the reflected light is collected by a camera or by a special holographic film. The second, known as the reference beam, is made to bounce from a mirror onto the collection plate without touching the object.
On the other hand the ray coming from the source interferes and mixes with the reflected one of the object. And lines are created on the plate, called interference fringes, which contain the information. Currently, the uses of traditional holography are quite limited and the resolutions of the images themselves are not very high.
“Classical holography does very clever things with the direction, colour and polarization of light, but it has limitations, such as interference from unwanted light sources and a strong sensitivity to mechanical instabilities,” said physicist Hugo Defienne.
Quantum Holograms
Physicists at the University of Glasgow were the first to use the unique properties of quantum entanglement to encode information in a hologram. In the new process, they used a laser light beam divided into two paths, but this time the rays are never reunited.
They did so by exploiting quantum entanglement, a phenomenon of quantum physics for which two particles, in this case, photons, are intrinsically connected in such a way that each state change of the first corresponds to an instantaneous change of the other, regardless of distance.
Through coupled plates of a special beta barium borate crystal, physicists split a beam of blue-violet laser light and created entangled photons. A beam of photons was directed at a target object. The other beam, on the other hand, was directed towards a spatial light modulator, an optical device that can slow down the speed of light fractionally. The photons were slowed down before they were collected by a second camera.
This slight slowing thus altered the phase of the photons, giving rise to one of the most surprising aspects of this innovative method. Unlike traditional holography, with the new technique, the two-photon beams never overlap.
The hologram is created by measuring the correlations between the positions of the entangled photons and using two separate digital cameras. Finally, the four resulting holograms are combined to create a high-resolution phase image.
This way scientists were able to generate holograms of the University of Glasgow logo amongst many others. “The process we have developed frees us from those limits of classical coherence and introduces holography into the quantum realm.
The use of entangled photons offers new ways to create sharper and more detailed holograms, which open up new possibilities for practical applications of the technique, “explained Defienne.
Possible Applications
This innovative technique has the potential to be used in various scientific fields. It could improve medical imaging. “Our process allows for the creation of high-resolution, lower-noise images, which could help detect the finer details of cells and help us learn more about how biology works at the cellular level,” said Defienne.
Furthermore, the discovery could represent a turning point in the new frontier of information, in particular for quantum communication networks. Daniele Faccio, another researcher at the University of Glasgow and co-author of the study, explained that the sensors of the CCD cameras they used for the experiments have unprecedented levels of resolution, i.e. up to 10,000 pixels for the image of each photon is entangled.
Thanks to this resolution, the researchers were able to measure the number of photons in the streams, as well as their entanglement, with truly remarkable precision.
At the Swiss Institute for Disruptive Innovation we strongly believe that Quantum computers and communication networks of the future will require at least that level of detail about the entangled particles they will use.
According Mr. Faccio: “it takes us one step closer to enabling real change in those rapidly developing sectors. It’s a really exciting breakthrough and we look forward to building on this success with further refinements”.
