A few years ago, Edward Snowden, a contractor working for the US National Security Agency, leaked documents that showed the ways in which intelligence agencies were spying on our data. One of the most striking revelations was that spies had tapped into fiber-optic cables to monitor the vast amounts of information flowing through them.
Snowden’s revelations have spurred efforts to tap the almost mystical properties of quantum science to make such hacking impossible. Now there are signs of progress.
A startup called Quantum Xchange says it has struck a deal giving it access to 500 miles (805 kilometers) of fiber-optic cable running along the east coast of the US to create what it claims will be the country’s first quantum key distribution (QKD) network.
Also, this week the University of Chicago, Argonne National Laboratory, and the Fermi National Accelerator Laboratory announced a joint venture to create a test bed for an approach to secure data communication using quantum teleportation.
The QKD approach used by Quantum Xchange works by sending an encoded message in classical bits while the keys to decode it are sent in the form of quantum bits, or qubits. These are typically photons, which travel easily along fiber-optic cables. The beauty of this approach is that any attempt to snoop on a qubit immediately destroys its delicate quantum state, wiping out the information it carries and leaving a telltale sign of an intrusion.
The initial leg of the network, linking New York City to New Jersey, will allow banks and other businesses to ship information between offices in Manhattan and data centers and other locations outside the city.
However, sending quantum keys over long distances requires “trusted nodes,” which are similar to repeaters that boost signals in a standard data cable. Quantum Xchange says it will have 13 of these along its full network. At nodes, keys are decrypted into classical bits and then returned to a quantum state for onward transmission. In theory, a hacker could steal them while they are briefly vulnerable.
Quantum teleportation eliminates this risk by exploiting a phenomenon known as entanglement. This involves creating a pair of qubits—again, typically photons—in a single quantum state. A change in one photon immediately influences the state of the linked one, even if they are very far away from one another. In theory, data transmission based on this phenomenon is unhackable because tampering with one of the qubits destroys their quantum state . (For a more detailed description of quantum teleportation, see “Inside Europe’s quest to build an unhackable quantum internet.”)
The challenges of making this work in practice are immense, and the approach is still confined to science labs. “Sending a photon into a piece of fiber is not a big deal,” says David Awschalom, a professor at the University of Chicago, “but creating and sustaining entanglement is really challenging.” That’s especially true over long-distance cable networks.
Awschalom is leading the initiative involving the university and the national laboratories. The aim, he says, is to have the test bed enable a “plug-and-play” approach that will let researchers evaluate various techniques for entangling and sending out qubits.
The test bed, which will be built with several million dollars from the US Department of Energy and use a 30-mile stretch of fiber-optic cable running between the labs, will be operated by members of the Chicago Quantum Exchange, which brings together 70 scientists and engineers from the three institutions.
Both Europe and China are also experimenting with quantum communications networks. Awschalom thinks it’s good to have healthy competition in the field. “Other countries have pushed forward to build [quantum] infrastructure,” he says. “Now we’ll do the same.”