A new technique involving entangled photons just led to a world first. Physicists overcome a big–limitation of traditional holography by using quantum mechanics to successfully encode information in a hologram.
This could lead to a big upgrade to holography, from entertainment purposes to more serious applications like medical imaging.
“Classical holography does very-clever things with the direction, color & polarization of light, but it has some limitations like interference from unwanted light sources & strong sensitivity to mechanical instabilities,” said physicist Hugo Defienne of University of Glasgow in Scotland.
“The process we have developed frees-us from those limitations of classical coherence & ushers holography into quantum realm. Using entangled photons offers new ways to make sharper, more-richly detailed holograms, which open-up new possibilities for practical applications of the technique.”
Holograms are something many of us see every-day. In simple terms, they are made by manipulating light to produce a 2D representation of a 3D image.
They are used for security purposes on banknotes, bankcards & passports, but their applications range widely, from art & entertainment to navigation to medical imaging.
The potential uses are exciting. Data storage is one that’s still being worked on. When the kinks are ironed-out, holographic memory might be next big thing in high-capacity data storage.
To make a hologram in the traditional way, a beam of laser light is split in two. At the source, two beams are coherent, that’s, the frequency & phase are the same. One beam called object beam, is reflected-off the object to be rendered. This reflected light is directed-to a collection plate.
The other beam called reference beam, is simply directed straight-to the collection plate. At this point, two beams mix & create an interference pattern. The difference in phase between the two beams, what allows a hologram to be created.
Defienne & his team use a similar set-up, with a split beam of laser light. But rather than directing both beams to one collection plate, they tried harnessing quantum entanglement. This is often a phenomenon where-by pairs of particles, in this case photons (particles of light), become linked in such way that actions performed on one affect the another, even at a significant distance.
Entangled photons can be often created by shining a higher energy laser light through paired beta barium borate crystal plates. This splits the photon into 2 entangled photons, each with half the energy of the original photon. So what the team did is this, starting with a violet-blue laser.
One beam, as per the traditional holography was directed to an object before being collected-by a megapixel digital camera. However, another beam of entangled photons was directed-to a spatial light modulator, which very slightly slowed the photons as they passed through, before they were collected-by a second camera.
This slight slow-down altered the phase of the photons, compared to the object beam. This meant that two beams didn’t got to overlap, the hologram is made by measuring correlations between the entangled photon positions in the two cameras. Finally, 4 holograms are combined for a high-resolution phase image.
“Many significant discoveries in optical quantum physics in recent years are made using simple, single-pixel sensors. They have the advantage of being small, quick & affordable, but their disadvantage is that they capture-only very limited data about the state of the entangled photons involved in the process. It might take an unprecedented amount of time to capture the extent of detail we can collect in a single image,” explained physicist Daniele Faccio of University of Glasgow.
“The CCD sensors that we are using give us an unprecedented amount of resolution to play with up to 10,000 pixels per image of each entangled photon. It means that we can measure the quality of their entanglement and the quantity of the photons in the beams with the remarkable accuracy.”
The team used their new technique to create holograms of University of Glasgow logo, also real 3D items like a strip of Scotch tape & part of a bird’s feather.
This demonstrates the technique potential use for measuring biological structures. It could even enable a new sort of microscopy with a large field of view, among other potential uses.
“One of those applications could be in medical imaging, where holography is already-used in microscopy to scrutinise details of delicate samples which are near-transparent,” Defienne said.
“Our process allows the creation of higher-resolution, lower-noise images, which could help reveal finer-details of cells and help us learn more about how biology functions at the cellular level.”
The research has been published in Nature Physics.