From Physics magazine:
By Erika K. Carlson
Advances in quantum information science have brought on the possibility of a quantum internet—networks that carry information via photons in superpositions of states, called qubits, rather than the 0’s and 1’s that today’s networks shuttle from place to place.
In the last decade or so, researchers around the world have taken big steps toward building quantum networks. While many groups have started testing small networks tens of miles in size, major obstacles, including the need to develop a key piece of hardware, lie in the way of larger quantum networks. “There’s still lots of research to be demonstrated,” says Gabriella Carini of Brookhaven National Laboratory, New York, an organizer of a “Quantum Internet Blueprint Workshop” that took place in February. “But if you don’t have a vision, all the pieces won’t talk together.” The workshop was a step toward “establishing a nationwide quantum internet” in the US, an effort that has gained momentum with the National Quantum Initiative Act in 2018 and the recent budget request by the Trump administration to fund plans for a quantum internet.
The appeal of quantum networks lies in both immediately practical applications and potential advances for basic science research. One of the clearest applications is the ability to send secure messages without the threat of eavesdroppers. Because information is encoded with superpositions of states, any interception of a message would make qubits’ wave functions collapse, signaling that the message was intercepted.
Qubits can also encode more information than classical bits, so quantum networks could potentially carry higher densities of information more efficiently. “It’s a fundamentally new way to connect information,” says David Awschalom, a researcher at the University of Chicago and Argonne National Laboratory who is working on a quantum network effort in the Chicago area. Quantum networks could advance developments in remote-sensing technology and telescopes as well as applications that scientists don’t yet realize. A quantum internet could be “another revolution at the same level as the classical internet,” Carini says.
However, the same properties that make quantum networks useful present significant challenges. Ground-based networks, whether classical or quantum, often use optical fibers to direct information from place to place in the form of photons. As photons travel through a network, some will be lost over time as a result of impurities in the fibers, weakening the signal. In classical networks, devices called “repeaters” intermittently detect the signal, amplify it, and send it off again. But for information carried by photons in superpositions of states, or qubits, “it’s not possible to read the signal without perturbing it,” Awschalom says.
Read more at Physics magazine.