Particles of distorted light that have been entangled using quantum mechanics offer a new approach to dense and secure data storage.
Holograms, which create three-dimensional images and serve as security features on credit cards, are typically created using patterns created by beams of laser light. In recent years, physicists have found ways to create holograms with entangled photons instead. Now this is literally a new twist in technology.
Entangled photons moving in a corkscrew fashion have created holograms that offer the possibility of dense and ultra-secure data encryption, researchers report in a study published in Physical Review Letters .
Light can travel in a variety of ways, including up-down and side-to-side patterns of polarized light. But when it carries a type of spin known as orbital angular momentum, it can also spread out in spirals that resemble twisted rotini.
Like any other photons, the twisted versions can be entangled so that they essentially act as one. Something that affects one of the entangled pair of photons instantly affects the other, even if they are very far apart.
In previous experiments, researchers sent data over the air in entangled pairs of twisted photons. This approach should provide high data rates because light can arrive with different amounts of twist, with each twist serving as a separate communication channel.
Now the same approach is applied to recording data in holograms. Instead of transmitting information along several twisted light channels, pairs of photons with different amounts of twist create different sets of data in a single hologram. The more angular momentum orbital states, each with a different amount of twist, the more data researchers can pack into a hologram.
In addition to the fact that holograms contain more data, increasing the variety of rotations used to record data increases security. Anyone who wants to read the information must know or guess how the light that recorded it was twisted.
For a hologram based on two types of convolutions, says physicist Xiangdong Zhang of the Beijing Institute of Technology, you’d need to choose the right combination of convolutions out of about 80 options to decode the data. Adding to the combinations of seven different spins opens up millions of possibilities. According to Zhang, this should be enough for our quantum holographic encryption system to have a sufficient level of security.”
The researchers demonstrated their technique by encoding words and letters into holograms and rereading the data using distorted light. Although the researchers created images from holographic data, says physicist Hugo Defien of the Paris Institute of Nanosciences, the memory itself should not be confused with holographic images.
DeFiennes, who was not involved in the new research, says that other quantum holography schemes, such as his efforts with polarized photons, produce direct images of objects, including microscopic structures.
“[Їх] the idea is very different there. . . from our approach in that sense,” Defrien says. “They use holography to store information,” rather than creating the usual three-dimensional images that most people associate with holograms.
The twisted-light data storage that Zhang and his colleagues demonstrated is slow, taking nearly 20 minutes to decipher an image of the acronym “BIT” for the Beijing Institute of Technology, where the experiments were conducted. And the safety demonstrated by the researchers is still relatively low, as they only included up to six forms of distorted light in their experiments.
Zhang is confident that both limitations can be overcome with technical improvements. “We think our technology has potential applications in quantum information encryption,” he says, “especially in quantum image encryption.”
