Researchers aiming to create a secure quantum version of the internet need a device called a quantum repeater, which doesn’t yet exist – but now two teams say they are well on the way to building one
By Alex Wilkins
15 May 2024
Quantum networks could spread across a city
Fit Ztudio/Shutterstock
Efforts to build a global quantum internet have received a boost from two developments in quantum information storage that could one day make it possible to communicate securely across hundreds or thousands of kilometres.
The internet as it exists today involves sending strings of digital bits, or 0s and 1s, in the form of electrical or optical signals, to transmit information. A quantum internet, which could be used to send unhackable communications or link up quantum computers, would use quantum bits instead. These rely on a quantum property called entanglement, a phenomenon in which particles can be linked and measuring one particle instantly influences the state of another, no matter how far apart they are.
Read more
Being in two places at once could make a quantum battery charge faster
Advertisement
Sending these entangled quantum bits, or qubits, over very long distances, requires a quantum repeater, a piece of hardware that can store the entangled state in memory and reproduce it to transmit it further down the line. These would have to be placed at various points on a long-distance network to ensure a signal gets from A to B without being degraded.
Quantum repeaters don’t yet exist, but two groups of researchers have now demonstrated long-lasting entanglement memory in quantum networks over tens of kilometres, which are the key characteristics needed for such a device.
Can Knaut at Harvard University and his colleagues set up a quantum network consisting of two nodes separated by a loop of optical fibre that spans 35 kilometres across the city of Boston. Each node contains both a communication qubit, used to transmit information, and a memory qubit, which can store the quantum state for up to a second. “Our experiment really put us in a position where we’re really close to working on a quantum repeater demonstration,” says Knaut.