Quantum, communication
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  • Wits researchers, with Chinese colleagues, have developed a technique to transport tweaked “spiral light” securely down off-the-shelf cable. This breakthrough opens a new avenue for researchers trying to communicate using quantum technology.
  • Quantum communication – which takes advantage of the “spooky” ability of two particles to affect each other, even though they are separated by vast distances – is a secure way to send information.
  • The new method means that researchers do not have to develop custom fibres to transport multiple “twisted” qubits, the quantum-mechanical versions of ordinary computing bits, and now we can securely communicate via legacy infrastructure.
  • For more stories, go to Business Insiders SA's home page.

It is now possible to send many twisted qubits of quantum-encoded information along conventional optical fibre.  

The breakthrough – by scientists from the University of the Witwatersrand in South Africa and Huazhang University of Science and Technology in Wuhan, China – overcomes a major impediment to the field of quantum networks: no one thought to transfer multiple quantum states down a conventional fibre link.  

Quantum communication, which takes advantage of the “quirky” behaviour of light particles, allows for truly secure information transfer. The communication hinges on a phenomenon called quantum entanglement, which occurs when the properties of two light particles are linked so that when one is measured, it affects the behaviour of the other – even though they may be on opposite sides of the Universe. This “quirk” also makes it possible to detect eavesdropping, because you can tell when one of the particles has been observed. 

Researchers had previously sent quantum-encoded data down optical cables, but at a very low rate, explains Prof Andrew Forbes, a physicist at Wits University and an author on the paper. “We want more information capacity, but that needs higher [quantum] dimensions, but was not possible on a legacy network.” 

The team manipulated properties of two light particles, altering the “pattern” of the one and the “polarisation” of the other, effectively “twisting” it. This tricked the light into travelling down the fibre, which is normally would not have travelled down. And, although there was only one particle of light travelling down the line, it could have an infinite number of patterns. 

The research was published on Friday in Science Advances

The researchers demonstrated this entanglement over 250 metres of fibre, and Forbes says it should be possible to do it over 100 kilometres. “This is the next step, along with new protocols to exploit this approach,” he says.

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