Scientists at Heriot-Watt University have published new research into the phenomenon known as quantum entanglement. 

This is when two particles – such as photons of light – remain connected even when they’re separated by vast distances.

Researches at Heriot-Watt’s Institute of Photonic and Quantum Sciences say that quantum entanglement will allow future communications networks to be unhackable, offering the most secure form of communication possible, even if divides are unsafe or in criminal hands. 

“The efficient and trusted flow of information lies at the heart of modern society today,” Professor Professor Mehul Malik, an experimental physicist and Professor of Physics at Heriot-Watt’s School of Engineering and Physical Sciences says. “In the future, quantum networks will provide a way to have ultra-secure, high-capacity communication.

However, entangled photons can be disrupted over long distances, by noisy real-world environments such as stormy weather, background noise, or signal loss in a communications network – jeopardising security. 

“Even the best optical fibers in the world will have a certain amount of loss per kilometer, so this is a big hurdle in making this form of quantum communication possible,” explains Professor Malik.

Working with colleagues at the University of Geneva in Switzerland, Heriot-Watt physicists have developed a way for quantum entanglement to survive and remain robust under even extreme conditions of noise and loss.

“This is the first time it’s been shown that quantum entanglement can tolerate both noise and loss – and still survive in a strong form known as quantum steering,” Malik continued. 

Quantum technology involves harnessing the physics of sub-atomic particles to develop ultra-high performance applications including more powerful computing, more secure communications and more reliable navigation systems.

The research team at the Beyond Binary Quantum Information Lab were able to improve the robustness of entanglement by using photons entangled in multiple dimensions (qudits), compared to the standard two-dimensional quantum units (qubits). 

This ‘high-dimensional’ entanglement uses the spatial structure of light to entangle photons in a 53-dimensional space made up of ‘pixels’ of light.

In a test, the researchers were able to steer the entangled photons through loss and noise conditions equivalent to 79km of telecoms fibre optic cable, with 36% of ‘white noise’ – noise that could come from sunlight leaking into the experiment, for example.

Interestingly, the research also found that, counter-intuitively, increasing the number of dimensions in quantum entanglement also dramatically reduces the time it takes to measure the results. 

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The full results of the research have been published in the scientific journal Physical Review X, a journal of the American Physical Society. 

The research is funded by the QuantERA Programme, the Engineering and Physical Sciences Research Council (EPSRC), the European Research Council (ERC), and the Swiss National Science Foundation. 

Professor Malik says: “Quantum technology is very much an emerging area that’s being advanced by both academia and industry, and I think our research is incredibly relevant to both.

“The efficient and trusted flow of information lies at the heart of modern society today,” Malik adds.

Quantum networks, Malik says, can ensure these flows are highly powerful and secure.

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