Photons for Stronger Cyber Security

Senior Research Fellow James Grieve of the Centre for Quantum Technologies at NUS and Amelia Tan, Senior R&D Researcher of Trustwave, use entangled photons for improved cyber security. (Source: CQT, NUS)

Beneath many cities are complex networks of optical fibres that carry data to offices and homes. Researchers from the National University of Singa­pore (NUS) and Singtel, Asia’s leading communi­cations technology group, have demonstrated a technique that will help pairs of light particles smoothly navigate these networks, an approach that will enable stronger cyber security. The demons­tration was performed over 10km of Singtel’s fibre network. This project, conducted in Singapore, is driven by the NUS-Singtel Cyber Security Research & Development Labora­tory. It relies on the expertise from the Centre for Quantum Techno­logies (CQT) at NUS.

This new approach supports the deployment of quantum key distri­bution (QKD). Detection of individual photons creates encryption keys for secure communi­cation. Data encrypted with such keys is resistant to all computa­tional hacks. QKD trials are being conducted worldwide as governments and companies recognise the need to strengthen their cyber security. The QKD trials carried out by the NUS-Singtel team use pairs of photons that are connected by the quantum property of entangle­ment. Most QKD schemes require that the sender and receiver of a secret message exchange photons directly or trust the source of their keys. With this alter­native approach, it is possible to check the security of a key provided by a third party supplier.

It works like this: the 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 fibre segments and junction boxes. On their paths, the photons also suffer dispersion, where they effectively spread out. This affects the operators’ ability to track the photons.

The new trick keeps the entangled photons in sync as they travel different paths through the network. This is important because they are 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,” says James Grieve, a researcher on the team.

The technique works by carefully designing the photon source to create pairs of light particles with zero-dispersion wave­length. Normally, in optical fibres bluer light would arrive faster than redder light, spreading out the photons’ arrival times. Working around the zero-dispersion point makes it possible to match the speeds through the photons’ time-energy ent­anglement. Then the timing is preserved.

Alexander Ling, a Principal Inves­tigator at CQT, led this work for the NUS-Singtel lab. He said, “Before these results, it was not known if the multi-segment nature of deployed fibre would enable high precision dispersion cancel­lation, because the segments don’t generally have identical zero dispersion wave­lengths.”

In showing it can work, the team boosts expec­tations for QKD over commercial fibre. The entangled photons could find other appli­cations, too. For example, the photons in each pair are created within femto­seconds of each other. Their coor­dinated arrival times might synchronise clocks for time-critical operations such as financial trading. (Source: CQT, NUS)

Reference: J. A. Grieve et al.: Characterizing nonlocal dispersion compensation in deployed telecommunications fiber, Appl. Phys. Lett. 114, 131106 (2019); DOI: 10.1063/1.5088830

Link: Centre for Quantum Technologies, National University of Singapore, Singapore

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