28th December 2024 Quantum teleportation achieved over Internet cable A study in Optica reports the first demonstration of quantum teleportation over fibres carrying conventional telecommunications traffic.
Engineers at Northwestern University in Chicago, Illinois, are the first to successfully demonstrate quantum teleportation over a fibre-optic cable already carrying Internet traffic. Their study is published this month in the journal Optica. This breakthrough introduces the new possibility of combining quantum communication with existing Internet cables – greatly simplifying the infrastructure required for distributed quantum sensing or computing applications. "This is incredibly exciting because nobody thought it was possible," said Prem Kumar, Professor of Electrical and Computer Engineering at Northwestern, who led the research. "Our work shows a path towards next-generation quantum and classical networks sharing a unified fibre-optic infrastructure. Basically, it opens the door to pushing quantum communications to the next level." Quantum teleportation could revolutionise communication networks by enabling the transfer of quantum states across vast distances, paving the way for ultra‑secure communication and distributed quantum computing. This could drastically enhance future global data exchanges and enable a new, absolutely secure way to share information. The process works by harnessing quantum entanglement – a technique in which two particles are linked, regardless of distance between them. Instead of transmitting physical particles, quantum teleportation allows for the transfer of a quantum state using entanglement, ensuring that measurement outcomes remain correlated between distant locations. Since quantum states collapse upon measurement, any attempt to intercept data would disturb the system, making eavesdropping detectable. In other words, such a network would be theoretically unhackable, offering unprecedented levels of data security. "In optical communications, all signals are converted to light," Kumar explained. "While conventional signals for classical communications typically comprise millions of particles of light, quantum information uses single photons." "By performing a destructive measurement on two photons – one carrying a quantum state and one entangled with another photon – the quantum state is transferred onto the remaining photon, which can be very far away," said Jordan Thomas, a PhD candidate in Kumar's laboratory and first author. "The photon itself does not have to be sent over long distances, but its state still ends up encoded onto the distant photon. Teleportation allows the exchange of information over great distances without requiring the information itself to travel that distance." Until now, many researchers had doubted the possibility of quantum teleportation in cables carrying classical communications. The entangled photons would drown among the millions of other light particles, rather like a flimsy bicycle trying to pass through a crowded tunnel of speeding, heavy-duty trucks. Kumar and his team, however, found a way to help the delicate photons steer clear of the busy traffic. After conducting in-depth studies of how light scatters within fibre-optic cables, the researchers found a less crowded wavelength of light to place their photons. Then, they added special filters to reduce noise from regular Internet traffic. "We carefully studied how light is scattered, and placed our photons at a judicial point where that scattering mechanism is minimised," said Kumar. "We found we could perform quantum communication without interference from the classical channels that are simultaneously present." To test the new method, Kumar and his team set up a 30-kilometre-long fibre-optic cable – running between two of Northwestern's campuses – with a photon at either end. They then simultaneously sent quantum information and 400 gigabits per second (Gbps) Internet traffic through it. Finally, they measured the quality of the quantum information at the receiving end while executing the teleportation protocol by making quantum measurements at the mid-point. The researchers found the quantum information had been successfully transmitted – even with busy Internet traffic whizzing by. "Although many groups have investigated the co-existence of quantum and classical communications in fibre, this work is the first to show quantum teleportation in this new scenario," said Thomas. "This ability to send information without direct transmission opens the door for even more advanced quantum applications being performed without dedicated fibre." Next, Kumar plans to extend the experiments over longer distances. He also plans to use two pairs of entangled photons, rather than one pair, to demonstrate entanglement swapping, another important milestone leading to distributed quantum applications. "Quantum teleportation has the ability to provide quantum connectivity securely between geographically distant nodes," added Kumar. "But many people have long assumed that nobody would build specialised infrastructure to send particles of light. If we choose the wavelengths properly, we won't have to build new infrastructure. Classical communications and quantum communications can co-exist."
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