Entangled Photons Strengthen Data Encryption

By keeping entangled photons in sync as they travel different paths through an optical fiber network, researchers in Singapore have demonstrated successful quantum key distribution over a distance of ten kilometers.

AsianScientist (Apr. 17, 2019) – In a study published in Applied Physics Letters, researchers at the National University of Singapore have devised a method to perform quantum key distribution (QKD) over optical fiber networks.

Beneath many cities are complex networks of optical fibers that carry data, encoded in pulses of light, to offices and homes. Researchers have given much thought about how such data can be better secured, and in recent years, the concept of QKD has gained traction as a means to better encrypt information.

In the present study, researchers led by Associate Professor Alexander Ling of the National University of Singapore (NUS), in collaboration with Singapore telecommunications provider Singtel, have demonstrated a technique that will help pairs of light particles, known as photons, smoothly navigate fiber optic networks.

In essence, a supplier would create a pair of photons, then split them up, sending one each to the two parties that want to communicate securely. The entanglement means that when the parties measure their photons, they get matching results, either a 0 or 1. Doing this for many photons leaves each party with identical patterns of 0s and 1s, giving them a key to lock and unlock a message.

Typically, each photon encounters a different obstacle course of spliced fiber segments and junction boxes. On their paths, the photons also suffer dispersion, where they effectively spread out. This affects the communicating parties’ ability to track the photons.

What the NUS researchers have managed to do is keep the entangled photons in sync as they travel different paths through the network. This in turn allows the photons to be identified by the gap between their arrival times at the detector.

“Timing information is what allows us to link pairs of detection events together. Preserving this correlation will help us to create encryption keys faster,” said Dr. James Grieve at NUS, a co-author on the study.

The researchers demonstrated their technology over ten kilometers of Singtel’s fiber network, successfully encrypting and transmitting information between two locations.

The article can be found at: Grieve et al. (2019) Characterizing Nonlocal Dispersion Compensation in Deployed Telecommunications Fiber.


Source: National University of Singapore.
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