What are Quantum Networks and How Do They Work?

Developing quantum communications is a great advance in securing data transfer, but if you don’t build a network to facilitate the exchange of information, the effectiveness and utility of that communication is limited.

Similar to the way classical networks exchange communications and data between different inter-connected entities, a quantum network enables the secure transmission and exchange of quantum communications (quantum cryptographic keys) over fiber optic cable between distinct, physically-separated quantum processors, or endpoints.

Quantum Xchange is working on developing the first quantum network in the U.S, specifically using Quantum Key Distribution (QKD) technology.  So far, the company has secured approximately 800km of fiber optic cable along the east coast to build the network, from Boston to Washington D.C., with the goal of extending it across the entire U.S.  The first leg of the QKD network, connecting New York City to New Jersey, has been operational and accepting customers since November 2018.

Quantum Xchange’s CEO John Prisco explains the preliminary vision behind his company’s quantum network, which it has named Phio: “Organizations with offices in Boston will be able to send secure communications to a partner in D.C., and eventually even further – as the goal is to keep buying up optical fiber that is already in the ground all over the country so that we can provide a secure quantum network that will serve the entire nation.”  He further stressed the critical need to  establish a quantum key distribution network as a defensive measure “before the unprecedented power of quantum computers become an offensive weapon.”

The Quantum Network, explained:

How quantum encryption works - quantum networksThe QKD network works by transmitting an encoded key in the form of quantum bits (qubits)  between endpoints over a fiber optic cable.   The qubits are typically polarized photons, which can travel easily along fiber-optic cables.  Any attempt to intercept the quantum key destroys the qubit’s delicate quantum state and the information it holds, alerting the endpoints that an intrusion occurred.  The detectability of the intrusions is what ensures the security of the transmission.

The trick, or rather the challenge, of a quantum network is that quantum communications are limited by the distance photons can travel over fiber-optic cable, normally around 100km.  To solve this problem, Quantum Xchange has developed “trusted nodes”, which operate the same way a repeater does in a traditional communications network.  At each node, the key is decrypted into classical bits and then put back into its quantum state for further transmission to the next node.

The global race is on to develop quantum capabilities – quantum computers, quantum cryptography, quantum-safe cryptography, quantum communication.  Building quantum networks is yet another step in the process. Europe has already made some strides toward this goal, though the shorter distances in Europe make it less of a challenge.  Now the U.S. is showing progress as well, with Quantum Xchange’s Phio network and associated trusted node technology.

Curious about how quantum communication works? Read our explainer here.