Researchers have used a quantum mechanical property to overcome some of the limitations of conventional holograms. The new approach, detailed in Nature Physics, employed quantum entanglement, allowing two photons to become a single “non-local particle.” A series of entangled photon pairs is key to producing new and improved holograms.
Classical holograms work by using a single light beam split into two. One beam is sent towards the object you’re recreating and is reflected onto a special camera. The second beam is sent directly onto the camera. By measuring the differences in light, its phase, you can reconstruct a 3D image. A key property in this is the wave’s coherence.
The quantum hologram shares some of these principles but its execution is very different. It starts by splitting a laser beam in two, but these two beams will not be reunited. The key is in the splitting. As you can see in the image below, the blue laser hits a nonlinear crystal, which creates two beams made of pairs of entangled photons.
Entanglement has no equivalent in our macroscopic world. Particles that are entangled are part of a single state, so a change to one of them creates an instantaneous change to the others no matter how far apart they might be. One entangled photon beam is sent through the object, while the other is sent through a special light modulator.
As the two beams are measured independently with separate megapixel cameras, their properties will have changed in very specific ways due to the effects of quantum mechanics and four images will be collected. The data is then combined into a hologram, even though the beams remain forever parted.
“Classical holography does very clever things with the direction, colour and polarisation of light, but it has limitations, such as interference from unwanted light sources and strong sensitivity to mechanical instabilities,” lead study author Dr Hugo Defienne from the University of Glasgow (UofG) said in a statement.
“The process we’ve developed frees us from those limitations of classical coherence and ushers holography into the quantum realm. Using entangled photons offers new ways to create sharper, more richly detailed holograms, which open up new possibilities for practical applications of the technique.”
The team's experiment was able to recreate holograms of a liquid crystal sporting the letters “UofG” as well as recreate transparent tape, silicone oil droplets, and a bird feather. The experimental technology could have important applications in multiple fields beyond what current holograms can achieve.
“One of those applications could be in medical imaging, where holography is already used in microscopy to scrutinize details of delicate samples which are often near-transparent. 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,” Dr Defienne explained.
The work could also be important for quantum computers and quantum communication. Prototypes of these technologies regularly employ entangled photons.